Motion vector prediction method and apparatus for encoding or decoding video

ABSTRACT

Provided are a motion vector predicting method and an apparatus for encoding and decoding a video. The motion vector prediction method includes: determining, from neighboring blocks of the current block, a plurality of candidate blocks that are referred to so as to predict a motion vector of a current block; determining a candidate motion vector of a first candidate block among the determined plurality of candidate blocks, based on whether a reference image of the first candidate block and a reference image of the current block are long-term reference images; and determining the motion vector of the current block by using a candidate motion vector list including the determined candidate motion vector of the first candidate block and candidate motion vectors from remaining candidate blocks among the determined plurality of candidate blocks.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 14/412,556, filed Jan. 2, 2015, which claims thebenefit of a National Stage application under 35 U.S.C. § 371 ofPCT/KR2013/005866, filed on Jul. 2, 2013, which claims the benefit ofU.S. Provisional Application No. 61/667,133, filed on Jul. 2, 2012, allthe disclosures of which are incorporated herein in their entireties byreference.

BACKGROUND 1. Field

Apparatuses and methods consistent with exemplary embodiments relate toencoding and decoding a video, and more particularly, to encoding anddecoding a video by performing inter prediction and/or motioncompensation.

2. Description of the Related Art

As hardware for reproducing and storing high resolution or high qualityvideo content is being developed and supplied, a need for a video codecfor effectively encoding or decoding the high resolution or high qualityvideo content is increasing. In a related art video codec, a video isencoded according to a limited encoding method based on a macroblockhaving a predetermined size.

Image data in a spatial domain is converted into coefficients in afrequency domain by using frequency transformation. In a video codec, animage is split into blocks having a predetermined size and discretecosine transform (DCT) is performed on each block to encode frequencycoefficients in a block unit so as to quickly perform frequencytransformation. The coefficients in the frequency domain are easilycompressed compared to the image data in the spatial domain. Inparticular, since an image pixel value in the spatial domain isexpressed in a prediction error via inter prediction or intra predictionof the video codec, a large amount of data may be converted to 0 whenfrequency transformation is performed on the prediction error. The videocodec replaces data that continuously and repeatedly occurs by datahaving a small size, thereby reducing an amount of data.

SUMMARY

Aspects of one or more exemplary embodiments provide a method andapparatus for determining a motion vector via motion vector prediction,and provide a method and apparatus for encoding a video accompanied byinter prediction and motion compensation via motion vector predictionand a method and apparatus for decoding a video accompanied by motioncompensation via motion vector prediction.

According to an aspect of an exemplary embodiment, there is provided amotion vector prediction method for inter prediction, the motion vectorprediction method including: determining, from among neighboring blocksof a current block, a plurality of candidate blocks that are referred toso as to predict a motion vector of the current block; determining acandidate motion vector of a first candidate block among the determinedplurality of candidate blocks, based on whether a reference image of thefirst candidate block and a reference image of the current block arelong-term reference images; and determining the motion vector of thecurrent block by using a candidate motion vector list including thedetermined candidate motion vector of the first candidate block andcandidate motion vectors from remaining candidate blocks among thedetermined plurality of candidate blocks.

According to an aspect of another exemplary embodiment, there isprovided a motion vector prediction apparatus for inter prediction, themotion vector prediction apparatus including: a candidate blockdeterminer configured to determine, from neighboring blocks of a currentblock, a plurality of candidate blocks that are referred to so as topredict a motion vector of the current block, and determining acandidate motion vector of a first candidate block among the determinedplurality of candidate blocks, based on whether a reference image of thefirst candidate block and a reference image of the current block arelong-term reference images; and a motion vector determiner configured todetermine the motion vector of the current block by using a candidatemotion vector list including the determined candidate motion vector ofthe first candidate block and candidate motion vectors from remainingcandidate blocks among the determined plurality of candidate blocks.

According to aspects of one or more exemplary embodiments, when at leastone of a current block and reference images of the current block is along-term reference image, an operation of adjusting a size of a motionvector of a candidate block or an operation of referring to the motionvector of the candidate block is omitted and the current block may bepredicted by referring to a motion vector of another candidate blockhaving relatively high prediction accuracy. Accordingly, efficiency ofoperations of predicting a motion vector may be improved.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a motion vector prediction apparatusaccording to an exemplary embodiment;

FIG. 2 is a flowchart illustrating a motion vector prediction methodaccording to an exemplary embodiment;

FIG. 3 illustrates neighboring blocks spatially adjacent to a currentblock, according to an exemplary embodiment;

FIG. 4A is a diagram for describing a case when a candidate block is acollocated block of another image, according to an exemplary embodiment;

FIG. 4B is a diagram for describing a case when a candidate block is aneighboring block of a same image, according to an exemplary embodiment;

FIG. 5 is a flowchart illustrating a video encoding method accompaniedby a motion vector prediction method, according to an exemplaryembodiment;

FIG. 6 is a flowchart illustrating a video decoding method accompaniedby a motion vector prediction method, according to an exemplaryembodiment;

FIG. 7 is a block diagram of a video encoder including a motion vectorprediction apparatus, according to an exemplary embodiment;

FIG. 8 is a block diagram of a video decoder including a motion vectorprediction apparatus, according to an exemplary embodiment;

FIG. 9 is a block diagram of a video encoding apparatus based on codingunits according to a tree structure, according to an exemplaryembodiment;

FIG. 10 is a block diagram of a video decoding apparatus based on codingunits according to a tree structure, according to an exemplaryembodiment;

FIG. 11 is a diagram for describing a concept of coding units accordingto an exemplary embodiment;

FIG. 12 is a block diagram of an image encoder based on coding unitsaccording to an exemplary embodiment;

FIG. 13 is a block diagram of an image decoder based on coding unitsaccording to an exemplary embodiment;

FIG. 14 is a diagram illustrating deeper coding units according todepths, and partitions according to an exemplary embodiment;

FIG. 15 is a diagram for describing a relationship between a coding unitand transformation units, according to an exemplary embodiment;

FIG. 16 is a diagram for describing encoding information of coding unitscorresponding to a coded depth, according to an exemplary embodiment;

FIG. 17 is a diagram of deeper coding units according to depths,according to an exemplary embodiment;

FIGS. 18 through 20 are diagrams for describing a relationship betweencoding units, prediction units, and transformation units, according toan exemplary embodiment;

FIG. 21 is a diagram for describing a relationship between a codingunit, a prediction unit, and a transformation unit, according toencoding mode information of Table 1;

FIG. 22 is a diagram of a physical structure of a disc in which aprogram is stored, according to an exemplary embodiment;

FIG. 23 is a diagram of a disc drive for recording and reading a programby using a disc;

FIG. 24 is a diagram of an overall structure of a content supply systemfor providing a content distribution service;

FIGS. 25 and 26 are diagrams respectively of an external structure andan internal structure of a mobile phone to which a video encoding methodand a video decoding method are applied, according to an exemplaryembodiment;

FIG. 27 is a diagram of a digital broadcast system to which acommunication system is applied, according to an exemplary embodiment;and

FIG. 28 is a diagram illustrating a network structure of a cloudcomputing system using a video encoding apparatus and a video decodingapparatus, according to an exemplary embodiment.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, a motion vector prediction apparatus and a motion vectordetermining method according to one or more exemplary embodiments willbe described with reference to FIGS. 1 through 4B. Also, video encodingand decoding methods and video encoding and decoding apparatusesaccompanied by a motion vector prediction method, according to one ormore exemplary embodiments, will be described with reference to FIGS. 5and 8. Also, video encoding operations and video decoding operationsaccompanied by motion vector prediction operations and based on codingunits having a tree structure, according to one or more exemplaryembodiments, will be described with reference to FIGS. 9 through 21.Hereinafter, an ‘image’ may denote a still image or a moving image of avideo, or a video itself.

A motion vector prediction apparatus and a motion vector determiningmethod according to one or more exemplary embodiments will be describedwith reference to FIGS. 1 through 4B. Furthermore, video encoding anddecoding methods and video encoding and decoding apparatuses, which areaccompanied by a motion vector prediction method, according to one ormore exemplary embodiments will be described with reference to FIGS. 5and 8.

FIG. 1 is a block diagram of a motion vector prediction apparatus 10according to an exemplary embodiment.

The motion vector prediction apparatus 10 includes a candidate blockdeterminer 12 and a motion vector determiner 14.

Inter prediction uses similarity between a current image and anotherimage. A reference region similar to a current region of the currentimage is detected from a reference image restored prior to the currentimage. A distance between the current region and the reference region oncoordinates is expressed in a motion vector, and a difference betweenpixel values of the current region and the reference region is expressedas residual data. Accordingly, instead of directly outputting imageinformation of the current region, an index indicating the referenceimage, the motion vector, and the residual data may be output via interprediction of the current region.

The motion vector prediction apparatus 10 according to an exemplaryembodiment may perform inter prediction according to blocks of eachimage of a video. A block may have a square shape, a rectangular shape,or an arbitrary geometrical shape, and is not limited to a data unithaving a predetermined size. The block according to an exemplaryembodiment may be a maximum coding unit, a coding unit, a predictionunit, or a transformation unit, among coding units according to a treestructure. Video encoding and decoding operations based on coding unitsaccording to a tree structure will be described later with reference toFIGS. 9 through 21.

The reference image used for inter prediction of the current image mustbe decoded prior to the current image. The reference image for interprediction according to an exemplary embodiment may be classified into ashort-term reference image and a long-term reference image. A decodedpicture buffer stores restored images generated via motion compensationof previous images. The generated restored images may be used as thereference images for inter prediction of other images. Accordingly, atleast one short-term reference image or at least one long-term referenceimage for inter prediction of the current image may be selected fromamong the restored images stored in the decoded picture buffer. Theshort-term reference image may be an image decoded immediately orrecently prior to the current image according to a decoding order,whereas the long-term reference image may be an image decoded long priorto the current image but is selected and stored in the decoded picturebuffer to be used as the reference image for inter prediction of otherimages.

A motion vector of a current block may be determined by referring to amotion vector of another block for motion vector prediction, predictionunit (PU) merging, or advanced motion vector prediction (AMVP).

The motion vector prediction apparatus 10 may determine a motion vectorof a current block by referring to a motion vector of another blockspatially or temporally adjacent to the current block. The motion vectorprediction apparatus 10 may determine a candidate motion vector listincluding a plurality of motion vectors of candidate blocks that may bereferred to. The motion vector prediction apparatus 10 may determine themotion vector of the current block by referring to one motion vectorselected from the candidate motion vector list.

The candidate block determiner 12 may determine a plurality of candidateblocks that may be referred to so as to predict the motion vector of thecurrent block, from among neighboring blocks surrounding the currentblock.

A candidate block according to one or more exemplary embodiments may bea neighboring block adjacent to the current block in a current image ofthe current block, or a collocated block at a same location as thecurrent block in an image restored prior to the current image.

The motion vector determiner 14 may generate the candidate motion vectorlist including candidate motion vectors of the plurality of candidateblocks being referred to so as to predict the motion vector of thecurrent block.

The motion vector determiner 14 may determine a motion vector of acandidate block among the plurality of candidate blocks as a candidatemotion vector to be one in the candidate motion vector list, based onwhether a reference image of the candidate block and a reference imageof the current block are each a long-term reference image. The motionvector determiner 14 may select a current motion vector of a candidateblock as a candidate motion vector, or scale a current motion vector andthen select the scaled current motion vector as a candidate motionvector. The determined candidate motion vector may be included in thecandidate motion vector list.

When the reference image of the candidate block is different from thereference image of the current block, the motion vector determiner 14may determine whether the reference image of the current block and thereference image of the candidate block are each a long-term referenceimage. The motion vector determiner 14 may determine how to use themotion vector of the candidate block based on whether the referenceimages of the current block and candidate block are each a short-termreference image or a long-term reference image.

When the reference image of the current block and the reference image ofthe candidate block are both long-term reference images, the motionvector determiner 14 may determine a current motion vector of thecandidate block as a candidate motion vector. Here, the current motionvector of the candidate block is included in the candidate motion vectorlist without scaling.

When the reference image of the current block and the reference image ofthe candidate block are both short-term reference image, the motionvector determiner 14 may scale a current motion vector of the candidateblock. Here, the candidate block determiner 12 may scale the currentmotion vector of the candidate block based on a ratio of a distancebetween the current image and the reference image of the current blockand a distance between an image of the candidate block and the referenceimage of the candidate block. The motion vector determiner 14 mayinclude the scaled current motion vector of the candidate block in thecandidate motion vector list.

When one of the reference image of the current block and the referenceimage of the candidate block is a short-term reference image and theother one is a long-term reference image, the motion vector determiner14 may determine not to use the motion vector of the candidate block asa candidate motion vector of the candidate motion vector list. Referencepossibility information of the candidate block may be set to a disabledstate.

Alternatively, when one of the reference image of the current block andthe reference image of the candidate block is a short-term referenceimage and the other one is a long-term reference image, the candidatemotion vector of the first candidate block may be set to 0.

The motion vector determiner 14 may determine at least one candidatemotion vector from the candidate motion vector list, and determine themotion vector of the current block by using the selected at least onecandidate motion vector. The motion vector determiner 14 may copy,combine, or modify the at least one candidate motion vector to determinethe motion vector of the current block.

FIG. 2 is a flowchart illustrating a motion vector prediction methodaccording to an exemplary embodiment.

A motion vector of a current block may be predicted by using a motionvector of a block temporally or spatially adjacent to the current blockby using the motion vector prediction apparatus 10 according to anexemplary embodiment. Alternatively, a plurality of candidate blockscapable of predicting a motion vector may be determined, one of thecandidate blocks may be selected, and a motion vector of a current blockmay be determined by referring to a motion vector of the selectedcandidate block.

When a reference image indicated by a reference index of a predeterminedcandidate block from among candidate blocks is different from areference image of a current block and the motion vector predictionapparatus 10 predicts a motion vector of the current block by referringto a motion vector of the predetermined candidate block, accuracy of thepredicted motion vector may be low even when the motion vector of thepredetermined candidate block is scaled. Accordingly, when the referenceimage of the current block and the reference image of the predeterminedcandidate block are different from each other, the motion vectorprediction apparatus 10 may determine whether to scale and refer to themotion vector of the predetermined candidate block or whether not torefer to the corresponding motion vector.

The motion vector prediction method, wherein a motion vector of acurrent block is predicted from a motion vector of a candidate block bythe motion vector prediction apparatus 10, will now be described withreference to operations 21, 23, and 25 of FIG. 2.

In operation 21, the motion vector prediction apparatus 10 may determinecandidate blocks to be referred to, from neighboring blocks spatiallyadjacent to a current block or from blocks at the same location as thecurrent block from among images temporally prior to or next to a currentimage.

In operation 23, the motion vector prediction apparatus 10 may determinea motion vector of a first candidate block as a candidate motion vectorof the current block based on whether the reference image of the currentblock and a reference image of the first candidate block are each along-term reference image.

In operation 25, the motion vector prediction apparatus 10 may determinea candidate motion vector list including the candidate motion vector ofthe first candidate block and candidate motion vectors from remainingcandidate blocks. The motion vector prediction apparatus 10 maydetermine the motion vector of the current block by using at least onecandidate motion vector in the candidate motion vector list.

When the reference image of the first candidate block is different fromthe reference image of the current block, the motion vector predictionapparatus 10 may determine whether to use the motion vector of the firstcandidate block as a candidate motion vector in the candidate motionvector list based on whether the reference image of the current blockand the reference image of the first candidate block are each ashort-term reference image or a long-term reference image.

The motion vector prediction apparatus 10 may determine whether thereference image of the current block is a long-term reference image byusing a long-term reference index indicating whether the reference imageof the current block is a long-term reference image. Similarly, it isdetermined whether the reference image of the first candidate block is along-term reference image by using a long-term reference index of thefirst candidate block.

In operation 25, when the reference images of the current block and thefirst candidate block are both long-term reference images, the motionvector prediction apparatus 10 may include a current motion vector ofthe first candidate block in the candidate motion vector list withoutscaling the current motion vector of the first candidate block.

In operation 25, when one of the reference images is a short-termreference image and the other one is a long-term reference image, it maybe determined that the motion vector of the first candidate block is notused in the candidate motion vector list.

In operation 25, when both of the reference images are short-termreference images, the current motion vector of the first candidate blockmay be scaled according to a ratio of a distance between the referenceimages of the current image and the current block and a distance betweenan image of the first candidate block and the reference image of thefirst candidate block. The scaled current motion vector may be includedin the candidate motion vector list.

The motion vector prediction apparatus 10 may determine the candidatemotion vector list via operations 21, 23, and 25. When only one of thereference images is a long-term reference image, the motion vectorprediction apparatus 10 excludes the motion vector of the firstcandidate block from the candidate motion vector list, and thus is notreferred to. Accordingly, the motion vector prediction apparatus 10 maydetermine the motion vector of the current block by referring toremaining motion vectors in the candidate motion vector list.

When both of the reference images are long-term reference images, themotion vector prediction apparatus 10 includes the motion vector of thefirst candidate block into the candidate motion vector list withoutscaling. Accordingly, the motion vector prediction apparatus 10 mayselect an optimum reference motion vector from among the motion vectorof the first candidate block and the remaining candidate motion vector,and determine the motion vector of the current block based on theselected optimum reference motion vector.

When both of the reference images are short-term reference images, themotion vector prediction apparatus 10 scales the current motion vectorof the first candidate block and includes the scaled current motionvector into the candidate motion vector list, as the candidate motionvector. Accordingly, the motion vector prediction apparatus 10 mayselect an optimum reference motion vector from among the candidatemotion vector of the first candidate block and the remaining candidatemotion vectors, and determine the motion vector of the current block byusing the selected optimum reference motion vector.

As described above, according to the motion vector prediction apparatus10 and the motion vector prediction method described above withreference to FIGS. 1 and 2, when at least one of the reference images isa long-term reference image, an operation of scaling a motion vector ofa candidate block or an operation of referring to a motion vector of acandidate block may be omitted.

In other words, if a motion vector of a current block is predicted byreferring to a motion vector of a candidate block when a reference imageof the current block and a reference image of the candidate block aredifferent from each other and at least one of the reference images is along-term reference image, accuracy of the predicted motion vector maybe low. Thus, an operation of referring to the motion vector of thecandidate block whose prediction accuracy is low may be omitted, and thecurrent block may be predicted by referring to a motion vector ofanother candidate block whose prediction accuracy is relatively high.Accordingly, efficiency of predicting a motion vector may be increased.

FIG. 3 illustrates neighboring blocks spatially adjacent to a currentblock 20, according to an exemplary embodiment.

In order to predict encoding information of the current block 20,encoding information of at least one of a block A₀ 21, a block A₁ 22, ablock B₀ 23, a block B₁ 24, and a block B₂ 25 from among neighboringblocks spatially adjacent to the current block 20 may be referred to. InFIG. 3, sizes of the block A₀ 21, the block A₁ 22, the block B₀ 23, theblock B₁ 24, and the block B₂ 25 do not show actual sizes of neighboringblocks. Here, the block A₀ 21, the block A₁ 22, the block B₀ 23, theblock B₁ 24, and the block B₂ 25 show blocks located in relativedirections with respect to the current block 20.

An x-coordinate of a block increases from left to right and any-coordinate of the block increases from top to bottom. The block A₀ 21may be a block including a sample whose x- and y-coordinates are bothsmaller than a bottom left sample. The block A₁ 22 may be a blockincluding samples whose x-coordinate is smaller than but y-coordinate isthe same as the bottom left sample. The block B₀ 23 may be a blockincluding a sample whose x- and y-coordinates are both larger than a topright sample. The B₁ 24 may be a block including a sample whosey-coordinate is smaller than but x-coordinate is the same as the topright sample. The block B₂ 25 may be a block including a sample whose x-and y-coordinates are both smaller than a top left sample.

The motion vector prediction apparatus 10 may use the block A₀ 21, theblock A₁ 22, the block B₀ 23, the block B₁ 24, and the block B₂ 25 ascandidate blocks in order to predict a motion vector of the currentblock 20. Accordingly, the motion vector prediction apparatus 10 mayrefer to encoding information of the block A₀ 21, the block A₁ 22, theblock B₀ 23, the block B₁ 24, and the block B₂ 25 from among theneighboring blocks surrounding the current block 20.

The motion vector prediction apparatus 10 may determine a candidateblock which is to be a reference block of the current block and whoseprediction information is to be merged with prediction information ofthe current block 20 by using candidate motion vectors included in acandidate motion vector list. The prediction information of thedetermined candidate block may be encoded as prediction information ofthe current block.

For example, when encoding information of the block A₀ 21 from among theblock A₀ 21, the block A₁ 22, the block B₀ 23, the block B₁ 24, and theblock B₂ 25 is same as the encoding information of the current block 20,the current block 20 may be merged and encoded with the block A₀ 21. Bymerging the current block 20 and the block A₀ 21, an overlapping portionof the encoding information of the block A₀ 21 and the current block 20is not repeatedly encoded. Accordingly, when an encoder outputs theencoding information of the block A₀ 21, the encoding information of thecurrent block 20 may not be output again. Even when the encodinginformation of the current block 20 is not parsed while a receiverparses encoding information for blocks including the current block 20and the block A₀ 21, which are mutually merged, a decoder may decode thecurrent block 20 by using the encoding information parsed in advance forthe block A₀ 21.

The motion vector prediction apparatus 10 may predict a motion vector ofthe current block 20 by combining at least one of candidate motionvectors in a candidate motion vector list.

While predicting a motion vector, the motion vector of the current block20 may be determined by using the motion vectors of the block A₀ 21, theblock A₁ 22, the block B₀ 23, the block B₁ 24, and the block B₂ 25disposed adjacent to the current block 20. A motion vector estimator ofthe current block 20 may be determined by using motion vector estimatorsof the block A₀ 21, the block A₁ 22, the block B₀ 23, the block B₁ 24,and the block B₂ 25. Alternatively, the motion vector estimator of thecurrent block 20 may be determined by using a combination of two or moremotion vectors (motion vector estimators) of the block A₀ 21, the blockA₁ 22, the block B₀ 23, the block B₁ 24, and the block B₂ 25.

Accordingly, the motion vector (motion vector estimator) of the currentblock 20 may be predicted from at least one of the motion vectors(motion vector estimators) of the block A₀ 21, the block A₁ 22, theblock B₀ 23, the block B₁ 24, and the block B₂ 25. Accordingly, when anencoder first encodes and outputs the motion vectors (motion vectorestimators) of the block A₀ 21, the block A₁ 22, the block B₀ 23, theblock B₁ 24, and the block B₂ 25, the encoder may not encode the motionvector (motion vector estimator) of the current block 20. Even when themotion vector (motion vector estimator) of the current block 20 is notreceived, a decoder may predict the motion vector (motion vectorestimator) of the current block 20 by using at least one of the motionvectors (motion vector predictors) of the block A₀ 21, the block A₁ 22,the block B₀ 23, the block B₁ 24, and the block B₂ 25.

Hereinafter, a motion vector prediction scheme according to a type of acandidate block will be described with reference to FIGS. 4A and 4B.

FIG. 4A is a diagram for describing a case when a candidate block is acollocated block 36 of another image, according to an exemplaryembodiment.

A collocated image 35 is an image restored prior to a current image 30,and may be referred to for inter prediction of a current block 31 in thecurrent image 30. The collocated image 35 may be determined according toa collocated index 32 of the current block 31.

A block of the collocated image 35, which is at a same location as thecurrent block 31 of the current image 30, may be determined as thecollocated block 36. The motion vector prediction apparatus 10 may usethe collocated block 36 as a candidate block to be referred to so as topredict a motion vector 34 of the current block 31. Accordingly, themotion vector 34 of the current block 31 may be predicted by referringto a motion vector 37 of the collocated block 36.

A collocated reference image 38 may be determined according to pictureorder count (POC) indicated by a reference index of the collocated block36. A current reference image 33 may be determined according to POCindicated by a reference index of the current block 31.

However, when the collocated reference image 38 and the currentreference image 33 are different from each other, the motion vectorprediction apparatus 10 may determine again whether to refer to themotion vector 37 of the collocated block 36 or how to refer to themotion vector 37 of the collocated block 36.

In detail, when the reference index of the collocated block 36 and thereference index of the current block 31 are different from each other,the motion vector prediction apparatus 10 may determine whether thecollocated reference image 38 and the current reference image 33 areeach a short-term or long-term reference image by using long-termreference indexes of the collocated block 36 and current block 31.

However, when the collocated reference image 38 and the currentreference image 33 are different from each other, the motion vectorprediction apparatus 10 may again determine whether to refer to themotion vector 37 of the collocated block 36 or how to refer to themotion vector 37 of the collocated block 36.

When the current reference image 33 and the collocated reference image38 are different from each other but are both short-term referenceimages, the motion vector 37 of the collocated block 36 may be scaledbased on a ratio of a distance Td between the collocated image 35 andthe collocated reference image 38 and a distance Tb between the currentimage 30 and the current reference image 33. Here, the distance Tdbetween the current image 30 and the collocated reference image 38 maybe determined based on a difference value of POCs of the current image30 and collocated reference image 38. Similarly, the distance Tb betweenthe current image 30 and current reference image 33 may be determinedbased on a difference value of POCs of the current image 30 and currentreference image 33.

In other words, when the current reference image 33 and the collocatedreference image 38 are both short-term reference images, a candidatemotion vector MVcol′ may be updated to a value obtained by multiplyingthe motion vector 37 MVcol of the collocated block 36 by the ratio ofthe distance Td and the distance Tb. (MVcol′=MVcol*Tb/Td)

Accordingly, when the current reference image 33 and the collocatedreference image 38 are different from each other but are both short-termreference images, the motion vector prediction apparatus 10 may changethe motion vector 37 of the collocated block 36 in a candidate motionvector list to the candidate motion vector MVcol′.

When one of the current reference image 33 and the collocated referenceimage 38 is a short-term reference image and the other one is along-term reference image, a not-available flag may be assigned to themotion vector 37 of the collocated block 36. In this case, the motionvector 37 of the collocated block 36 may be excluded from the candidatemotion vector list of the current image 30.

When the current reference image 33 and the collocated reference image38 are both long-term reference images, the motion vector 37 of thecollocated block 36 may be maintained. In this case, the motion vector37 of the collocated block 36 may be maintained without scaling in thecandidate motion vector list.

FIG. 4B is a diagram for describing a case when a candidate block is aneighboring block 46 of a same image, according to an exemplaryembodiment.

The motion vector prediction apparatus 10 may use the neighboring block46 adjacent to a current block 41 in a current image 40, as a candidateblock to be referred to so as to predict a motion vector 44 of thecurrent block 41. Accordingly, the motion vector 44 of the current block41 may be predicted by referring to a motion vector 47 of theneighboring block 46.

A neighboring reference image 48 may be determined according to POCindicated by a reference index of the neighboring block 46. A currentreference image 43 may be determined according to POC indicated by areference index of a current block 41.

However, when the neighboring reference image 48 and the currentreference image 43 are different from each other, the motion vectorprediction apparatus 10 may again determine whether the motion vector 47of the neighboring block 46 is referred to, or how to refer to themotion vector 47 of the neighboring block 46.

In detail, when the reference index of the neighboring block 46 and thereference index of the current block 41 are different from each other,the motion vector prediction apparatus 10 may determine whether theneighboring block 46 and the current reference image 43 are each ashort-term or long-term reference image by using a long-term referenceindex of the neighboring block 46 and a long-term reference index of thecurrent block 41.

However, when the neighboring block 46 and the current reference image33 are different from each other, the motion vector prediction apparatus10 may determine whether to refer to the motion vector 47 of theneighboring block 46 or how to refer to the motion vector 47 of theneighboring block 46.

When the current reference image 43 and the neighboring reference image48 are different from each other but are both short-term referenceimages, the motion vector 47 of the neighboring block 46 may be scaledbased on a ratio of a distance Td between the current image 40 and theneighboring reference image 48 and a distance Tb between the currentimage 40 and the current reference image 43. Here, the distance Tdbetween the current image 40 and the neighboring reference image 48 maybe determined based on a difference value of POCs of the current image40 and neighboring reference image 48. Similarly, the distance Tbbetween the current image 40 and current reference image 43 may bedetermined based on a difference value of POCs of the current image 40and current reference image 43.

In other words, when the current reference image 43 and the neighboringreference image 48 are both short-term reference images, a candidatemotion vector MVne′ may be updated to a value obtained by multiplyingthe ratio of the distance Td and the distance Tb by the motion vector 47MVne of the collocated block 46. (MVne′=MVne*Tb/Td)

Accordingly, when the current reference image 43 and the neighboringreference image 48 are different from each other but are both short-termreference images, the motion vector prediction apparatus 10 may changethe motion vector 47 of the neighboring block 46 in a candidate motionvector list to the candidate motion vector MVne′.

When one of the current reference image 43 and the neighboring referenceimage 48 is a short-term reference image and the other one is along-term reference image, a not-available flag may be assigned to themotion vector 47 of the neighboring block 46. In this case, the motionvector 47 of the neighboring block 46 may be excluded from the candidatemotion vector list of the current image 40.

When the current reference image 43 and the neighboring reference image48 are both long-term reference images, the motion vector 47 of theneighboring block 46 may be maintained. In this case, the motion vector47 of the neighboring block 46 may be maintained without scaling in thecandidate motion vector list.

In FIGS. 4A and 4B, the motion vector prediction apparatus 10 maydetermine whether the current reference image 33 or 43 and a referenceimage (the collocated reference image 38 or neighboring reference image48) of a candidate block (the collocated block 36 or neighboring block46) are each a short-term or long-term reference image by using thelong-term reference indexes of the current block 31 or 41 and thecollocated block 36 or neighboring block 46, and determine whether torefer to the motion vector 37 or 47 of the collocated block 36 orneighboring block 46 or whether to refer to the motion vector 37 or 47of the collocated block 36 or neighboring block 46 after scaling.

A video encoding method and a video decoding method, which areaccompanied by a motion vector prediction method according to anexemplary embodiment, will now be described with reference to FIGS. 5and 6.

FIG. 5 is a flowchart illustrating a video encoding method accompaniedby a motion vector prediction method, according to an exemplaryembodiment.

In operation 51, a plurality of candidate blocks may be determined fromneighboring blocks of a current block, and motion vectors of thecandidate blocks may be determined as one or more candidate motionvectors of the current block based on whether reference images of thecurrent block and candidate blocks are each a long-term reference image,according to the motion vector prediction method.

When a reference image of a first candidate block in the candidateblocks is different from a reference image of the current block, it isdetermined whether to use a motion vector of the first candidate blockas it is or after scaling, based on whether the reference images of thecurrent block and first candidate block are each a long-term referenceimage.

When the reference images of the current block and first candidate blockare both long-term reference images, the motion vector of the firstcandidate block may be included into a candidate motion vector listwithout scaling.

When one of the reference images is a short-term reference image and theother one is a long-term reference image, it may be determined not touse the motion vector of the first candidate block in the candidatemotion vector list.

When the reference images are both short-term reference images, themotion vector of the first candidate block may be included into thecandidate motion vector list after scaling.

In operation 53, a candidate motion vector list including the candidatemotion vectors of the candidate blocks may be determined, and the motionvector of the current block may be determined by using at least onecandidate motion vector in the candidate motion vector list.

One candidate motion vector in the candidate motion vector list may beselected as a reference motion vector. The selected candidate motionvector may be modified prior to being determined as the reference motionvector. Alternatively, at least one candidate motion vector may beselected and combined to be determined as the motion vector of thecurrent block. For example, when there is different information of amotion vector, the difference information is synthesized to thereference motion vector so as to determine the motion vector of thecurrent block.

When a reference block indicated by the determined motion vector of thecurrent block is determined in a reference image of the current block,residual data between the reference block and the current block may begenerated.

In operation 55, the residual data is transformed and quantized togenerate quantized transformation coefficients.

Operations 51 through 55 may be performed according to blocks of thecurrent image, thereby generating quantized transformation coefficientsaccording to the blocks. Also, entropy encoding may be performed on thequantized transformation coefficients according to blocks so as togenerate and output a bitstream.

The video encoding method of FIG. 5 may be realized by a video encodingapparatus. Video encoding operations including inter prediction,transformation, and quantization may be performed as a video encodingprocessor executing the video encoding method of FIG. 5 is operated bybeing mounted in the video encoding apparatus or being externallycooperated with the video encoding apparatus. The video encodingprocessor of the video encoding apparatus may perform basic videoencoding processes as not only an individual processor, but also thevideo encoding apparatus, a central processing apparatus, or a graphicprocessing apparatus include a video encoding processing module.

FIG. 6 is a flowchart illustrating a video decoding method accompaniedby a motion vector prediction method, according to an exemplaryembodiment.

In operation 61, a reference index and quantized transformationcoefficients of a current block, and a motion vector of a candidateblock may be received.

In operation 63, dequantization and inverse transformation are performedon the quantized transformation coefficients of the current blockreceived in operation 61 to restore residual data of the current block.

In operation 65, candidate blocks to be referred to so as to predict amotion vector of the current block may be determined. A candidate motionvector of a first candidate block in the candidate blocks may bedetermined based on whether a reference image of the first candidateblock and a reference image of the current block are each a long-termreference image.

When the reference image of the current block and the reference image ofthe candidate block are both long-term reference images, the motionvector of the candidate block may be referred to without scaling.

When one of the reference images is a short-term reference image and theother one is a long-term reference image, the motion vector of the firstcandidate block may be determined not to be referred to.

When the reference images are both short-term reference images, themotion vector of the candidate block may be scaled and then referred to.

In operation 67, a candidate motion vector list including the candidatemotion vectors determined in operation 65 may be generated. A referencemotion vector may be determined by using at least one candidate motionvector in the candidate motion vector list. One candidate motion vectormay be selected and used as it is, or may be modified before being usedas the reference motion vector. Alternatively, at least one candidatemotion vector may be combined to be used as the reference motion vector.

A reference block indicated by the motion vector of the current blockmay be determined in a reference image of the current block indicated bythe received reference index of the current block. The current block maybe restored by synthesizing the residual data and the determinedreference block.

A current image including the restored current blocks may be restored byperforming operations 61 through 67 according to blocks. When images arerestored as such, a video including a sequence of restored images may berestored.

Operations 61 through 67 may be performed when a video is restored bydecoding an encoded bitstream upon receiving the encoded bitstreamduring video decoding operations. Here, in operation 61, the receivedencoded bitstream may be parsed and the reference index and thequantized transformation coefficients of the current block and themotion vector of the candidate block may be extracted from the parsedbitstream.

During the video encoding method described above with reference to FIG.5, operations 61 through 67 may also be performed in order to generate arestored image to be referred to for inter prediction of another image.Here, in operation 61, a reference index and quantized transformationcoefficients of a current block generated via inter prediction,transformation, and quantization, and a motion vector of a candidateblock are received, and then operations 63 through 67 are performed inorder to use a finally restored current image as a reference image forinter prediction of another image.

The video decoding method of FIG. 6 may be realized by a video decodingapparatus. Video decoding operations including dequantization, inversetransformation, and prediction/compensation may be performed as a videodecoding processor executing the video decoding method of FIG. 6 isoperated by being mounted in the video decoding apparatus or beingexternally cooperated with the video decoding apparatus. The videodecoding processor of the video decoding apparatus may perform basicvideo decoding processes as not only an individual processor, but alsothe video decoding apparatus, a central processing apparatus, or agraphic operation apparatus include a video decoding processing module.

A video encoder 70 and a video decoder 80 including the motion vectorprediction apparatus 10 according to an exemplary embodiment will now bedescribed with reference to FIGS. 7 and 8.

FIG. 7 is a block diagram of the video encoder 70 including the motionvector prediction apparatus 10, according to an exemplary embodiment.

The video encoder 70 may include an inter prediction unit 71 and atransformation quantization unit 75. The inter prediction unit 71 mayinclude the motion vector prediction apparatus 10 according to anexemplary embodiment, and a residual generator 73.

The motion vector prediction apparatus 10 determines a motion vectoraccording to blocks. Also, for motion vector prediction, predictionunits (PUs) merging, or Advanced Motion Vector Prediction (AMVP), amotion vector of a current block may be predicted by referring to amotion vector of another block. The motion vector prediction apparatus10 may determine a candidate motion vector list of the current block formotion vector prediction. One reference motion vector may be determinedfrom candidate motion vectors included in the candidate motion vectorlist.

The motion vector prediction apparatus 10 may determine how to refer toa motion vector of a first candidate block among the candidate blocks inthe candidate motion vector list based on whether a reference image ofthe first candidate block and a reference image of the current block areeach a long-term reference image.

The motion vector prediction apparatus 10 may determine a referencemotion vector by selecting an optimum candidate motion vector from thecandidate motion vectors in the candidate motion vector list, andpredict the motion vector of the current block by using the referencemotion vector.

The residual generator 73 may determine a reference block indicated bythe motion vector of the current block from the reference image of thecurrent block, and generate residual data between the reference blockand the current block.

Accordingly, the inter prediction unit 71 may output residual dataaccording to blocks by performing inter prediction according to blocks.

The transformation quantization unit 75 may generate quantizationtransformation coefficients by performing transformation andquantization on the residual data output by the inter prediction unit71. The transformation quantization unit 75 may generate quantizedtransformation coefficients according to blocks by performingtransformation and quantization on residual data according to blocksreceived from the inter prediction unit 71.

The video encoder 70 may output an encoded bitstream by performingentropy encoding on the quantized transformation coefficients generatedby the transformation quantization unit 75. Also, when a referenceindex, a motion vector, and a long-term reference index are output fromthe inter prediction unit 71, the video encoder 70 may output abitstream by performing entropy encoding not only on the quantizedtransformation coefficients, but also on the reference index, the motionvector, and the long-term reference index.

FIG. 8 is a block diagram of the video decoder 80 including the motionvector prediction apparatus 10, according to an exemplary embodiment.

The video decoder 80 includes a dequantization and inversetransformation unit 81 and a motion compensation unit 83. The interprediction unit 71 may include the motion vector prediction apparatus 10according to an exemplary embodiment and a block restorer 85.

The video decoder 80 may receive a reference index and quantizedtransformation coefficients of a current block, and a motion vector of acandidate block. The dequantization and inverse transformation unit 81may restore residual data of the current block by performingdequantization and inverse transformation on the received quantizedtransformation coefficients of the current block.

The motion compensation unit 83 may restore the current block byperforming motion compensation on the current block encoded via interprediction.

The motion vector prediction apparatus 10 determines a motion vectoraccording to blocks. The motion vector prediction apparatus 10 maydetermine a candidate motion vector list of the current block for motionvector prediction. A candidate block may be a collocated block or aneighboring block. The motion vector prediction apparatus 10 maydetermine one reference motion vector from candidate motion vectorsincluded in the candidate motion vector list.

The motion vector prediction apparatus 10 may determine how to refer toa motion vector of a first candidate block in the candidate blocks basedon whether a reference image of the first candidate block and areference image of the current block are each a long-term referenceimage.

The motion vector prediction apparatus 10 may determine a referencemotion vector by selecting an optimum candidate motion vector from thecandidate motion vectors in the candidate motion vector list, andpredict and determine the motion vector of the current block by usingthe reference motion vector.

The block restorer 85 may determine the reference image of the currentblock indicated by the reference index of the current block received bythe video decoder 80. The motion vector of the current block determinedby the motion vector prediction apparatus 10 indicates the referenceblock in the reference image, and the current block may be restored bysynthesizing the reference block and the residual data of the currentblock.

Accordingly, the motion compensation unit 83 may restore blocks byperforming motion compensation according to blocks, and restore acurrent image including the restored blocks. Accordingly, the videodecoder 80 may restore a video including an image sequence as images arerestored.

The video decoder 80 may further include an in-loop filtering unit thatperforms deblocking filtering on a restored current block and a restoredimage including restored blocks.

The video decoder 80 may restore a video by decoding an encodedbitstream upon receiving the encoded bitstream. Here, the video decoder80 may parse the received bitstream and extract the reference index andthe quantized transformation coefficients of the current block and themotion vector of the candidate block from the parsed bitstream. Also,the video decoder 80 may further include a receiver that receives abitstream, performs entropy decoding on the bitstream, and parsing andextracting the reference index and quantized transformation coefficientsof the current block, and the motion vector of the candidate block fromthe bitstream.

Also, the video decoder 80 may be combined to the video encoder 70 inorder for the video encoder 70 of FIG. 7 to generate a restored image tobe referred to for inter prediction of another image. Here, the videodecoder 80 may receive the reference index and the quantizedtransformation coefficients of the current block generated and outputvia inter prediction, transformation, and quantization by the videoencoder 70, and the motion vector of the candidate block, and output afinally restored current image through the dequantization and inversetransformation unit 81 and motion compensation unit 83. The restoredimage output by the video decoder 80 may be used as a reference imagefor inter prediction of another image by the video encoder 70.

As described above, the motion vector prediction apparatus 10 may spiltblocks of video data into coding units having a tree structure, andprediction units for inter prediction of coding units may be used.Hereinafter, a video encoding method, a video encoding apparatus, avideo decoding method, and a video decoding apparatus based on codingunits having a tree structure and transformation units will be describedwith reference to FIGS. 9 through 22.

FIG. 9 is a block diagram of a video encoding apparatus 100 based oncoding units according to a tree structure, according to an exemplaryembodiment.

The video encoding apparatus 100 based on coding units according to atree structure involving video prediction based on coding unitsaccording to a tree structure includes a maximum coding unit splitter110, a coding unit determiner 120, and an output unit 130. Forconvenience of explanation, “video encoding apparatus 100 based oncoding units according to a tree structure” is referred to as “videoencoding apparatus 100” hereinafter.

The maximum coding unit splitter 110 may split a current picture basedon a maximum coding unit that is a coding unit having a maximum size fora current picture of an image. If the current picture is larger than themaximum coding unit, image data of the current picture may be split intothe at least one maximum coding unit. The maximum coding unit accordingto an exemplary embodiment may be a data unit having a size of 32×32,64×64, 128×128, 256×256, etc., wherein a shape of the data unit is asquare having a width and length in squares of 2. The image data may beoutput to the coding unit determiner 120 according to the at least onemaximum coding unit.

A coding unit according to an exemplary embodiment may be characterizedby a maximum size and a depth. The depth denotes the number of times thecoding unit is spatially split from the maximum coding unit, and as thedepth deepens, deeper coding units according to depths may be split fromthe maximum coding unit to a minimum coding unit. A depth of the maximumcoding unit is an uppermost depth and a depth of the minimum coding unitis a lowermost depth. Since a size of a coding unit corresponding toeach depth decreases as the depth of the maximum coding unit deepens, acoding unit corresponding to an upper depth may include a plurality ofcoding units corresponding to lower depths.

As described above, the image data of the current picture is split intothe maximum coding units according to a maximum size of the coding unit,and each of the maximum coding units may include deeper coding unitsthat are split according to depths. Since the maximum coding unitaccording to an exemplary embodiment is split according to depths, theimage data of a spatial domain included in the maximum coding unit maybe hierarchically classified according to depths.

A maximum depth and a maximum size of a coding unit, which limit thetotal number of times a height and a width of the maximum coding unitare hierarchically split, may be predetermined.

The coding unit determiner 120 encodes at least one split regionobtained by splitting a region of the maximum coding unit according todepths, and determines a depth to output a finally encoded image dataaccording to the at least one split region. In other words, the codingunit determiner 120 determines a coded depth by encoding the image datain the deeper coding units according to depths, according to the maximumcoding unit of the current picture, and selecting a depth having theleast encoding error. The determined coded depth and the encoded imagedata according to the determined coded depth are output to the outputunit 130.

The image data in the maximum coding unit is encoded based on the deepercoding units corresponding to at least one depth equal to or below themaximum depth, and results of encoding the image data are compared basedon each of the deeper coding units. A depth having the least encodingerror may be selected after comparing encoding errors of the deepercoding units. At least one coded depth may be selected for each maximumcoding unit.

The size of the maximum coding unit is split as a coding unit ishierarchically split according to depths, and as the number of codingunits increases. Also, even if coding units correspond to the same depthin one maximum coding unit, it is determined whether to split each ofthe coding units corresponding to the same depth to a lower depth bymeasuring an encoding error of the image data of the each coding unit,separately. Accordingly, even when image data is included in one maximumcoding unit, the encoding errors may differ according to regions in theone maximum coding unit, and thus the coded depths may differ accordingto regions in the image data. Thus, one or more coded depths may bedetermined in one maximum coding unit, and the image data of the maximumcoding unit may be divided according to coding units of at least onecoded depth.

Accordingly, the coding unit determiner 120 may determine coding unitshaving a tree structure included in the maximum coding unit. The ‘codingunits having a tree structure’ according to one or more exemplaryembodiments include coding units corresponding to a depth determined tobe the coded depth, from among all deeper coding units included in themaximum coding unit. A coding unit of a coded depth may behierarchically determined according to depths in the same region of themaximum coding unit, and may be independently determined in differentregions. Similarly, a coded depth in a current region may beindependently determined from a coded depth in another region.

A maximum depth according to an exemplary embodiment is an index relatedto the number of splitting times from a maximum coding unit to a minimumcoding unit. A first maximum depth according to an exemplary embodimentmay denote the total number of splitting times from the maximum codingunit to the minimum coding unit. A second maximum depth according to anexemplary embodiment may denote the total number of depth levels fromthe maximum coding unit to the minimum coding unit. For example, when adepth of the maximum coding unit is 0, a depth of a coding unit, inwhich the maximum coding unit is split once, may be set to 1, and adepth of a coding unit, in which the maximum coding unit is split twice,may be set to 2. Here, if the minimum coding unit is a coding unit inwhich the maximum coding unit is split four times, 5 depth levels ofdepths 0, 1, 2, 3, and 4 exist, and thus the first maximum depth may beset to 4, and the second maximum depth may be set to 5.

Prediction encoding and transformation may be performed according to themaximum coding unit. The prediction encoding and the transformation arealso performed based on the deeper coding units according to a depthequal to or depths less than the maximum depth, according to the maximumcoding unit.

Since the number of deeper coding units increases whenever the maximumcoding unit is split according to depths, encoding, including theprediction encoding and the transformation, is performed on all of thedeeper coding units generated as the depth deepens. For convenience ofdescription, the prediction encoding and the transformation will now bedescribed based on a coding unit of a current depth, in a maximum codingunit.

The video encoding apparatus 100 may variously select a size or shape ofa data unit for encoding the image data. In order to encode the imagedata, operations, such as prediction encoding, transformation, andentropy encoding, are performed, and at this time, the same data unitmay be used for all operations or different data units may be used foreach operation.

For example, the video encoding apparatus 100 may select not only acoding unit for encoding the image data, but also a data unit differentfrom the coding unit so as to perform the prediction encoding on theimage data in the coding unit.

In order to perform prediction encoding in the maximum coding unit, theprediction encoding may be performed based on a coding unitcorresponding to a coded depth, i.e., based on a coding unit that is nolonger split to coding units corresponding to a lower depth.Hereinafter, the coding unit that is no longer split and becomes a basisunit for prediction encoding will now be referred to as a ‘predictionunit’. A partition obtained by splitting the prediction unit may includea prediction unit or a data unit obtained by splitting at least one of aheight and a width of the prediction unit. A partition is a data unitwhere a prediction unit of a coding unit is split, and a prediction unitmay be a partition having the same size as a coding unit.

For example, when a coding unit of 2N×2N (where N is a positive integer)is no longer split and becomes a prediction unit of 2N×2N, a size of apartition may be 2N×2N, 2N×N, N×2N, or N×N. Examples of a partition typeinclude symmetrical partitions that are obtained by symmetricallysplitting a height or width of the prediction unit, partitions obtainedby asymmetrically splitting the height or width of the prediction unit,such as 1:n or n:1, partitions that are obtained by geometricallysplitting the prediction unit, and partitions having arbitrary shapes.

A prediction mode of the prediction unit may be at least one of an intramode, a inter mode, and a skip mode. For example, the intra mode or theinter mode may be performed on the partition of 2N×2N, 2N×N, N×2N, orN×N. Also, the skip mode may be performed only on the partition of2N×2N. The encoding is independently performed on one prediction unit ina coding unit, thereby selecting a prediction mode having a leastencoding error.

The video encoding apparatus 100 may also perform the transformation onthe image data in a coding unit based not only on the coding unit forencoding the image data, but also based on a data unit that is differentfrom the coding unit. In order to perform the transformation in thecoding unit, the transformation may be performed based on a data unithaving a size smaller than or equal to the coding unit. For example, thedata unit for the transformation may include a data unit for an intramode and a data unit for an inter mode.

The transformation unit in the coding unit may be recursively split intosmaller sized regions in the similar manner as the coding unit accordingto the tree structure. Thus, residual data in the coding unit may bedivided according to the transformation unit having the tree structureaccording to transformation depths.

A transformation depth indicating the number of splitting times to reachthe transformation unit by splitting the height and width of the codingunit may also be set in the transformation unit. For example, in acurrent coding unit of 2N×2N, a transformation depth may be 0 when thesize of a transformation unit is 2N×2N, may be 1 when the size of thetransformation unit is N×N, and may be 2 when the size of thetransformation unit is N/2×N/2. In other words, the transformation unithaving the tree structure may be set according to the transformationdepths.

Encoding information according to coding units corresponding to a codeddepth requires not only information about the coded depth, but alsoabout information related to prediction encoding and transformation.Accordingly, the coding unit determiner 120 not only determines a codeddepth having a least encoding error, but also determines a partitiontype in a prediction unit, a prediction mode according to predictionunits, and a size of a transformation unit for transformation.

Coding units according to a tree structure in a maximum coding unit andmethods of determining a prediction unit/partition, and a transformationunit, according to an exemplary embodiment, will be described in detailbelow with reference to FIGS. 11 through 22.

The coding unit determiner 120 may measure an encoding error of deepercoding units according to depths by using Rate-Distortion Optimizationbased on Lagrangian multipliers.

The output unit 130 outputs the image data of the maximum coding unit,which is encoded based on the at least one coded depth determined by thecoding unit determiner 120, and information about the encoding modeaccording to the coded depth, in bitstreams.

The encoded image data may be obtained by encoding residual data of animage.

The information about the encoding mode according to coded depth mayinclude information about the coded depth, about the partition type inthe prediction unit, the prediction mode, and the size of thetransformation unit.

The information about the coded depth may be defined by using splitinformation according to depths, which indicates whether encoding isperformed on coding units of a lower depth instead of a current depth.If the current depth of the current coding unit is the coded depth,image data in the current coding unit is encoded and output, and thusthe split information may be defined not to split the current codingunit to a lower depth. Alternatively, if the current depth of thecurrent coding unit is not the coded depth, the encoding is performed onthe coding unit of the lower depth, and thus the split information maybe defined to split the current coding unit to obtain the coding unitsof the lower depth.

If the current depth is not the coded depth, encoding is performed onthe coding unit that is split into the coding unit of the lower depth.Since at least one coding unit of the lower depth exists in one codingunit of the current depth, the encoding is repeatedly performed on eachcoding unit of the lower depth, and thus the encoding may be recursivelyperformed for the coding units having the same depth.

Since the coding units having a tree structure are determined for onemaximum coding unit, and information about at least one encoding mode isdetermined for a coding unit of a coded depth, information about atleast one encoding mode may be determined for one maximum coding unit.Also, a coded depth of the image data of the maximum coding unit may bedifferent according to locations since the image data is hierarchicallysplit according to depths, and thus information about the coded depthand the encoding mode may be set for the image data.

Accordingly, the output unit 130 may assign encoding information about acorresponding coded depth and an encoding mode to at least one of thecoding unit, the prediction unit, and a minimum unit included in themaximum coding unit.

The minimum unit according to an exemplary embodiment is a square dataunit obtained by splitting the minimum coding unit constituting thelowermost depth by 4. Alternatively, the minimum unit according to anexemplary embodiment may be a maximum square data unit that may beincluded in all of the coding units, prediction units, partition units,and transformation units included in the maximum coding unit.

For example, the encoding information output by the output unit 130 maybe classified into encoding information according to deeper codingunits, and encoding information according to prediction units. Theencoding information according to the deeper coding units may includethe information about the prediction mode and about the size of thepartitions. The encoding information according to the prediction unitsmay include information about an estimated direction of an inter mode,about a reference image index of the inter mode, about a motion vector,about a chroma component of an intra mode, and about an interpolationmethod of the intra mode.

Information about a maximum size of the coding unit defined according topictures, slices, or GOPs, and information about a maximum depth may beinserted into a header of a bitstream, a sequence parameter set, or apicture parameter set.

Information about a maximum size of the transformation unit permittedwith respect to a current video, and information about a minimum size ofthe transformation unit may also be output through a header of abitstream, a sequence parameter set, or a picture parameter set. Theoutput unit 130 may encode and output reference information related toprediction, prediction information, and slice type information, whichare described above with reference to FIGS. 1 through 8.

In the video encoding apparatus 100, the deeper coding unit may be acoding unit obtained by dividing a height or width of a coding unit ofan upper depth, which is one layer above, by two. In other words, whenthe size of the coding unit of the current depth is 2N×2N, the size ofthe coding unit of the lower depth is N×N. Also, the coding unit withthe current depth having a size of 2N×2N may include a maximum of 4 ofthe coding units with the lower depth.

Accordingly, the video encoding apparatus 100 may form the coding unitshaving the tree structure by determining coding units having an optimumshape and an optimum size for each maximum coding unit, based on thesize of the maximum coding unit and the maximum depth determinedconsidering characteristics of the current picture. Also, since encodingmay be performed on each maximum coding unit by using any one of variousprediction modes and transformations, an optimum encoding mode may bedetermined considering characteristics of the coding unit of variousimage sizes.

Thus, if an image having a high resolution or a large data amount isencoded in a related art macroblock, the number of macroblocks perpicture excessively increases. Accordingly, the number of pieces ofcompressed information generated for each macroblock increases, and thusit is difficult to transmit the compressed information and datacompression efficiency decreases. However, by using the video encodingapparatus 100, image compression efficiency may be increased since acoding unit is adjusted while considering characteristics of an imagewhile increasing a maximum size of a coding unit while considering asize of the image.

The video encoding apparatus 100 of FIG. 9 may perform operations of themotion vector prediction apparatus 10 of FIG. 1 or the video encoder 70of FIG. 7.

The coding unit determiner 120 may determine a prediction unit includinga partition for inter prediction according to coding units having a treestructure for each maximum coding unit, and perform inter predictionunit.

The coding unit determiner 120 determines a motion vector according toprediction units. Also, for motion vector prediction, PU merging, orAMVP, a motion vector of a current prediction unit (partition) may bepredicted by referring to a motion vector of another prediction unit.The motion vector prediction apparatus 10 may determine a candidatemotion vector list of the current prediction unit for motion vectorprediction. One reference motion vector may be determined from candidatemotion vectors in the candidate motion vector list. A candidateprediction unit may be a neighboring prediction unit adjacent to thecurrent prediction unit or a collocated prediction unit in a collocatedimage.

The coding unit determiner 120 may determine how to refer to a motionvector of a first candidate prediction unit from among a plurality ofcandidate prediction units adjacent to the current prediction unit,based on whether a reference image of the first candidate predictionunit and a reference image of the current prediction unit are each along-term reference image.

It is determined whether the reference images are each a short-term or along-term reference image based on long-term reference indexes of thecurrent prediction unit and the first candidate prediction unit.

When the reference images are both long-term reference images, themotion vector of the candidate prediction unit may be referred to as itis without scaling.

When one of the reference images is a short-term reference image and theother one is a long-term reference image, it may be determined not torefer to the motion vector of the first candidate prediction unit.

When the reference images are both short-term reference images, themotion vector of the candidate prediction unit may be referred to afterscaling.

The coding unit determiner 120 may determine a reference motion vectorby selecting an optimum candidate motion vector from candidate motionvectors determined according to candidate blocks, and then predict anddetermine the motion vector of the current prediction unit by using thereference motion vector.

The coding unit determiner 120 may determine a reference block indicatedby the motion vector of the current block in the reference image of thecurrent prediction unit, and generate residual data between a referenceprediction unit and the current prediction unit.

Accordingly, the coding unit determiner 120 may output residual dataaccording to prediction units by performing inter prediction accordingto prediction units.

The coding unit determiner 120 may generate quantized transformationcoefficients by performing transformation and quantization ontransformation units of a coding unit including the residual dataaccording to prediction units. Accordingly, the coding unit determiner120 may generate quantized transformation coefficients according totransformation units.

The coding unit determiner 120 may perform operations of the videodecoder 80 described above with reference to FIG. 8 in order to generatea reference image for inter prediction of a prediction unit.

The coding unit determiner 120 may restore the residual data of thecurrent block by performing dequantization and inverse transformation onthe received quantized transformation coefficients of the currentprediction unit. The current prediction unit may be restored byperforming motion compensation on the current prediction unit encodedvia inter prediction.

As described above, the coding unit determiner 120 may determine how touse the motion vector of the first candidate prediction unit from amongthe plurality of candidate prediction units adjacent to the currentprediction unit, based on whether the reference image of the firstcandidate prediction unit and the reference image of the currentprediction unit are each a long-term reference image.

The coding unit determiner 120 may determine a reference motion vectorby selecting an optimum candidate motion vector from among the candidatemotion vectors included in the candidate motion vector list, and predictand determine the motion vector of the current prediction unit by usingthe reference motion vector.

The coding unit determiner 120 may determine the reference image of thecurrent prediction unit indicated by the received reference index of thecurrent prediction unit. The reference image of the current predictionunit may be determined according to POC indicated by the reference indexof the current prediction unit. A reference index indicates POCregardless of whether a reference image is a long-term or short-termreference image, and an image indicated by the POC may be determined asthe reference image.

A reference prediction unit indicated by the motion vector of thecurrent prediction unit is determined from the reference image, and thecurrent prediction unit may be restored by synthesizing the referenceprediction unit and residual data of the current prediction unit.

Accordingly, the coding unit determiner 120 may restore prediction unitsby performing motion compensation according to prediction units, andrestore a current image including the restored prediction units. Therestored prediction units and the restored current image may be referredto as another prediction image and another image.

FIG. 10 is a block diagram of a video decoding apparatus 200 based oncoding units according to a tree structure, according to an exemplaryembodiment.

The video decoding apparatus 200 based on coding units according to atree structure involves video prediction based on coding units having atree structure includes a receiver 210, an image data and encodinginformation extractor 220, and an image data decoder 230. Forconvenience of explanation, “video decoding apparatus 200 based oncoding units according to a tree structure” is referred to as “videodecoding apparatus 200” hereinafter.

Definitions of various terms, such as a coding unit, a depth, aprediction unit, a transformation unit, and information about variousencoding modes, for decoding operations of the video decoding apparatus200 are identical to those described with reference to FIG. 9 and thevideo encoding apparatus 100.

The receiver 210 receives and parses a bitstream of an encoded video.The image data and encoding information extractor 220 extracts encodedimage data for each coding unit from the parsed bitstream, wherein thecoding units have a tree structure according to each maximum codingunit, and outputs the extracted image data to the image data decoder230. The image data and encoding information extractor 220 may extractinformation about a maximum size of a coding unit of a current picture,from a header about the current picture, a sequence parameter set, or apicture parameter set.

Also, the image data and encoding information extractor 220 extractsinformation about a coded depth and an encoding mode for the codingunits having a tree structure according to each maximum coding unit,from the parsed bitstream. The extracted information about the codeddepth and the encoding mode is output to the image data decoder 230. Inother words, the image data in a bit stream is split into the maximumcoding unit so that the image data decoder 230 decodes the image datafor each maximum coding unit.

The information about the coded depth and the encoding mode according tothe maximum coding unit may be set for information about at least onecoding unit corresponding to the coded depth, and information about anencoding mode may include information about a partition type of acorresponding coding unit corresponding to the coded depth, about aprediction mode, and a size of a transformation unit. Also, splittinginformation according to depths may be extracted as the informationabout the coded depth.

The information about the coded depth and the encoding mode according toeach maximum coding unit extracted by the image data and encodinginformation extractor 220 is information about a coded depth and anencoding mode determined to generate a minimum encoding error when anencoder, such as the video encoding apparatus 100, repeatedly performsencoding for each deeper coding unit according to depths according toeach maximum coding unit. Accordingly, the video decoding apparatus 200may restore an image by decoding the image data according to a codeddepth and an encoding mode that generates the minimum encoding error.

Since encoding information about the coded depth and the encoding modemay be assigned to a predetermined data unit from among a correspondingcoding unit, a prediction unit, and a minimum unit, the image data andencoding information extractor 220 may extract the information about thecoded depth and the encoding mode according to the predetermined dataunits. If information about a coded depth and encoding mode of acorresponding maximum coding unit is recorded according to predetermineddata units, the predetermined data units to which the same informationabout the coded depth and the encoding mode is assigned may be inferredto be the data units included in the same maximum coding unit.

The image data decoder 230 restores the current picture by decoding theimage data in each maximum coding unit based on the information aboutthe coded depth and the encoding mode according to the maximum codingunits. In other words, the image data decoder 230 may decode the encodedimage data based on the extracted information about the partition type,the prediction mode, and the transformation unit for each coding unitfrom among the coding units having the tree structure included in eachmaximum coding unit. Decoding operations may include a predictionincluding intra prediction and motion compensation, and an inversetransformation.

The image data decoder 230 may perform intra prediction or motioncompensation according to a partition and a prediction mode of eachcoding unit, based on the information about the partition type and theprediction mode of the prediction unit of the coding unit according tocoded depths.

In addition, the image data decoder 230 may read information about atransformation unit according to a tree structure for each coding unitso as to perform inverse transformation based on transformation unitsfor each coding unit, for inverse transformation for each maximum codingunit. Via the inverse transformation, a pixel value of a spatial regionof the coding unit may be restored.

The image data decoder 230 may determine a coded depth of a currentmaximum coding unit by using split information according to depths. Ifthe split information indicates that image data is no longer split inthe current depth, the current depth is a coded depth. Accordingly, theimage data decoder 230 may decode encoded data in the current maximumcoding unit by using the information about the partition type of theprediction unit, the prediction mode, and the size of the transformationunit for each coding unit corresponding to the coded depth.

In other words, data units containing the encoding information includingthe same split information may be gathered by observing the encodinginformation set assigned for the predetermined data unit from among thecoding unit, the prediction unit, and the minimum unit, and the gathereddata units may be considered to be one data unit to be decoded by theimage data decoder 230 in the same encoding mode. As such, the currentcoding unit may be decoded by obtaining the information about theencoding mode for each coding unit.

Also, the image data decoder 230 of the video decoding apparatus 200 ofFIG. 10 may perform operations of the motion compensation apparatus 10of FIG. 1 or the video decoder 80 of FIG. 8.

The image data decoder 230 may determine the prediction unit for motioncompensation and perform motion compensation for each prediction unit,according to coding units having a tree structure, for each maximumcoding unit.

The image data decoder 230 may restore residual data of the currentblock by performing dequantization and inverse transformation onquantized transformation coefficients of a current prediction unit. Thecurrent prediction unit may be restored by performing motioncompensation on the current prediction unit encoded via interprediction.

The image data decoder 230 may determine whether a motion vector of afirst candidate prediction unit from among a plurality of candidateprediction units adjacent to the current prediction unit is to be usedas it is or after being modified based on whether a reference image ofthe first candidate prediction unit and a reference image of the currentprediction unit are each a long-term reference image.

A candidate prediction unit may be a neighboring prediction unitadjacent to a current prediction unit in a current image or a collocatedprediction unit in a collocated image.

It may be determined whether the reference images of the currentprediction unit and first candidate prediction unit are each ashort-term or long-term reference image based on long-term referenceindexes of the current prediction unit and first candidate predictionunit.

When the reference images are both long-term reference images, themotion vector of the first candidate prediction unit may be used as itis without scaling.

When one of the reference images is a short-term reference image and theother one is a long-term reference image, it may be determined not torefer to the motion vector of the first candidate prediction unit.

When the reference images are both short-term reference images, themotion vector of the first candidate prediction unit may be scaled to bedetermined as a candidate motion vector.

The image data decoder 230 may determine a candidate motion vector listincluding candidate motion vectors determined according to candidateblocks. A reference motion vector is determined by selecting an optimumcandidate motion vector from the candidate motion vector list, and themotion vector of the current block may be predicted and determined byusing the reference motion vector.

The image data decoder 230 may determine the reference image of thecurrent prediction unit according to POC indicated by a reference indexof the current prediction unit. A reference index indicates POCregardless of whether a reference image is a long-term or short-termreference image, and an image indicated by the POC may be determined asthe reference image.

A reference prediction unit indicated by the motion vector of thecurrent prediction unit is determined from the reference image, and thecurrent prediction unit may be restored by synthesizing the referenceprediction unit and the residual data of the current prediction unit.

Accordingly, the image data decoder 230 may restore prediction units byperforming motion compensation according to prediction units, andrestore a current image including the restored prediction unit.Accordingly, a video including an image sequence may be restored asimages are restored. The restored prediction unit and the restoredcurrent image may be referred to for another prediction unit and animage.

Thus, the video decoding apparatus 200 may obtain information about atleast one coding unit that generates the minimum encoding error whenencoding is recursively performed for each maximum coding unit, and mayuse the information to decode the current picture. In other words, thecoding units having the tree structure determined to be the optimumcoding units in each maximum coding unit may be decoded.

Accordingly, even if image data has high resolution and a large amountof data, the image data may be efficiently decoded and restored by usinga size of a coding unit and an encoding mode, which are adaptivelydetermined according to characteristics of the image data, by usinginformation about an optimum encoding mode received from an encoder.

FIG. 11 is a diagram for describing a concept of coding units accordingto an exemplary embodiment.

A size of a coding unit may be expressed by width×height, and may be64×64, 32×32, 16×16, and 8×8. A coding unit of 64×64 may be split intopartitions of 64×64, 64×32, 32×64, or 32×32, and a coding unit of 32×32may be split into partitions of 32×32, 32×16, 16×32, or 16×16, a codingunit of 16×16 may be split into partitions of 16×16, 16×8, 8×16, or 8×8,and a coding unit of 8×8 may be split into partitions of 8×8, 8×4, 4×8,or 4×4.

In video data 310, a resolution is 1920×1080, a maximum size of a codingunit is 64, and a maximum depth is 2. In video data 320, a resolution is1920×1080, a maximum size of a coding unit is 64, and a maximum depth is3. In video data 330, a resolution is 352×288, a maximum size of acoding unit is 16, and a maximum depth is 1. The maximum depth shown inFIG. 11 denotes a total number of splits from a maximum coding unit to aminimum decoding unit.

If a resolution is high or a data amount is large, a maximum size of acoding unit may be large so as to not only increase encoding efficiencybut also to accurately reflect characteristics of an image. Accordingly,the maximum size of the coding unit of the video data 310 and 320 havinga higher resolution than the video data 330 may be 64.

Since the maximum depth of the video data 310 is 2, coding units 315 ofthe video data 310 may include a maximum coding unit having a long axissize of 64, and coding units having long axis sizes of 32 and 16 sincedepths are deepened to two layers by splitting the maximum coding unittwice. Since the maximum depth of the video data 330 is 1, coding units335 of the video data 330 may include a maximum coding unit having along axis size of 16, and coding units having a long axis size of 8since depths are deepened to one layer by splitting the maximum codingunit once.

Since the maximum depth of the video data 320 is 3, coding units 325 ofthe video data 320 may include a maximum coding unit having a long axissize of 64, and coding units having long axis sizes of 32, 16, and 8since the depths are deepened to 3 layers by splitting the maximumcoding unit three times. As a depth deepens, detailed information may beprecisely expressed.

FIG. 12 is a block diagram of an image encoder 400 based on coding unitsaccording to an exemplary embodiment.

The image encoder 400 performs operations of the coding unit determiner120 of the video encoding apparatus 100 to encode image data. In otherwords, an intra predictor 410 performs intra prediction on coding unitsin an intra mode, from among a current frame 405, and a motion estimator420 and a motion compensator 425 respectively perform inter estimationand motion compensation on coding units in an inter mode from among thecurrent frame 405 by using the current frame 405, and a reference frame495.

Data output from the intra predictor 410, the motion estimator 420, andthe motion compensator 425 is output as a quantized transformationcoefficient through a transformer 430 and a quantizer 440. The quantizedtransformation coefficient is restored as data in a spatial domainthrough a dequantizer 460 and an inverse transformer 470, and therestored data in the spatial domain is output as the reference frame 495after being post-processed through a deblocking unit 480 and a sampleadaptive offset (SAO) adjustor 490. The quantized transformationcoefficient may be output as a bitstream 455 through an entropy encoder450.

In order for the image encoder 400 to be applied in the video encodingapparatus 100, all elements of the image encoder 400, i.e., the intrapredictor 410, the motion estimator 420, the motion compensator 425, thetransformer 430, the quantizer 440, the entropy encoder 450, thedequantizer 460, the inverse transformer 470, the deblocking unit 480,and the SAO adjustor 490 perform operations based on each coding unitamong coding units having a tree structure while considering the maximumdepth of each maximum coding unit.

Specifically, the intra predictor 410, the motion estimator 420, and themotion compensator 425 determines partitions and a prediction mode ofeach coding unit from among the coding units having a tree structurewhile considering the maximum size and the maximum depth of a currentmaximum coding unit, and the transformer 430 determines the size of thetransformation unit in each coding unit from among the coding unitshaving a tree structure.

In detail, the motion estimator 420 may predict a motion vector of acurrent prediction unit (partition) by referring to a motion vector ofanother prediction unit for PU merging or AMVP. The motion estimator 420may predict a motion vector according to the motion vector predictionmethod described above with reference to FIGS. 1 through 4B.

The motion estimator 420 may determine a reference motion vector byselecting an optimum candidate motion vector from among candidate motionvectors included in a candidate motion vector list, and predict anddetermine the motion vector of the current prediction unit by using thereference motion vector. The motion estimator 420 may determine areference block indicated by the motion vector of the current block inthe reference frame 495 of the current prediction unit, and generateresidual data between the reference prediction unit and the currentprediction unit. Accordingly, the motion estimator 420 may output theresidual data according to prediction units.

Also, the motion compensator 425 may predict a motion vector accordingto the motion vector prediction method described above with reference toFIGS. 1 through 4B, and perform motion compensation by using the motionvector.

The motion compensator 425 may determine a reference prediction unitindicated by a motion vector of the current prediction unit, in thereference frame 495, and the current prediction unit may be restored bysynthesizing the reference prediction unit and the residual data of thecurrent prediction unit.

Accordingly, the motion compensator 425 may restore prediction units byperforming motion compensation according to prediction units, andrestore a current image including the restored prediction units. Therestored prediction unit and the restored image may be referred to foranother prediction unit and an image.

FIG. 13 is a block diagram of an image decoder 500 based on coding unitsaccording to an exemplary embodiment.

A parser 510 parses encoded image data to be decoded and informationabout encoding required for decoding from a bitstream 505. The encodedimage data is output as inverse quantized data through an entropydecoder 520 and a dequantizer 530, and the inverse quantized data isrestored to image data in a spatial domain through an inversetransformer 540.

An intra predictor 550 performs intra prediction on coding units in anintra mode with respect to the image data in the spatial domain, and amotion compensator 560 performs motion compensation on coding units inan inter mode by using a reference frame 585.

The image data in the spatial domain, which passed through the intrapredictor 550 and the motion compensator 560, may be output as arestored frame 595 after being post-processed through a deblocking unit570 and an SAO adjustor 580. Also, the image data that is post-processedthrough the deblocking unit 570 and the SAO adjustor 580 may be outputas the reference frame 585.

In order to decode the image data in the image data decoder 230 of thevideo decoding apparatus 200, the image decoder 500 may performoperations that are performed after the parser 510.

In order for the image decoder 500 to be applied in the video decodingapparatus 200, all elements of the image decoder 500, i.e., the parser510, the entropy decoder 520, the dequantizer 530, the inversetransformer 540, the intra predictor 550, the motion compensator 560,the deblocking unit 570, and the SAO adjustor 580 perform operationsbased on coding units having a tree structure for each maximum codingunit.

Specifically, the intra predictor 550 and the motion compensator 560perform operations based on partitions and a prediction mode for each ofthe coding units having a tree structure, and the inverse transformer540 perform operations based on a size of a transformation unit for eachcoding unit.

In detail, the motion compensator 560 may predict a motion vectoraccording to the motion vector prediction method described above withreference to FIGS. 1 through 4B. The motion compensator 560 maydetermine the reference frame 585 indicated by POC according to areference index of a current prediction unit, determine a referenceprediction unit indicated by the motion vector of the current predictionunit from the reference frame 585, and restore the current predictionunit by synthesizing the reference prediction unit and residual data ofthe current prediction unit.

Accordingly, the motion compensator 560 may restore prediction units byperforming motion compensation according to prediction units, andgenerate a restored image including the restored prediction units. Therestored prediction unit and the restored image may be referred to foranother prediction unit and another image.

FIG. 14 is a diagram illustrating deeper coding units according todepths, and partitions according to an exemplary embodiment.

The video encoding apparatus 100 and the video decoding apparatus 200use hierarchical coding units so as to consider characteristics of animage. A maximum height, a maximum width, and a maximum depth of codingunits may be adaptively determined according to the characteristics ofthe image, or may be differently set by a user. Sizes of deeper codingunits according to depths may be determined according to thepredetermined maximum size of the coding unit.

In a hierarchical structure 600 of coding units, according to anexemplary embodiment, the maximum height and the maximum width of thecoding units are each 64, and the maximum depth is 4. In this case, themaximum depth refers to a total number of times the coding unit is splitfrom the maximum coding unit to the minimum coding unit. Since a depthdeepens along a vertical axis of the hierarchical structure 600, aheight and a width of the deeper coding unit are each split. Also, aprediction unit and partitions, which are bases for prediction encodingof each deeper coding unit, are shown along a horizontal axis of thehierarchical structure 600.

In other words, a coding unit 610 is a maximum coding unit in thehierarchical structure 600, wherein a depth is 0 and a size, i.e., aheight by width, is 64×64. The depth deepens along the vertical axis,and a coding unit 620 having a size of 32×32 and a depth of 1, a codingunit 630 having a size of 16×16 and a depth of 2, and a coding unit 640having a size of 8×8 and a depth of 3. The coding unit 640 having a sizeof 8×8 and a depth of 3 is a coding unit having a lowest depth and aminimum coding unit.

The prediction unit and the partitions of a coding unit are arrangedalong the horizontal axis according to each depth. In other words, ifthe coding unit 610 having a size of 64×64 and a depth of 0 is aprediction unit, the prediction unit may be split into partitionsinclude in the encoding unit 610, i.e., a partition 610 having a size of64×64, partitions 612 having the size of 64×32, partitions 614 havingthe size of 32×64, or partitions 616 having the size of 32×32.

Similarly, a prediction unit of the coding unit 620 having the size of32×32 and the depth of 1 may be split into partitions included in thecoding unit 620, i.e., a partition 620 having a size of 32×32,partitions 622 having a size of 32×16, partitions 624 having a size of16×32, and partitions 626 having a size of 16×16.

Similarly, a prediction unit of the coding unit 630 having the size of16×16 and the depth of 2 may be split into partitions included in thecoding unit 630, i.e., a partition having a size of 16×16 included inthe coding unit 630, partitions 632 having a size of 16×8, partitions634 having a size of 8×16, and partitions 636 having a size of 8×8.

Similarly, a prediction unit of the coding unit 640 having the size of8×8 and the depth of 3 may be split into partitions included in thecoding unit 640, i.e., a partition having a size of 8×8 included in thecoding unit 640, partitions 642 having a size of 8×4, partitions 644having a size of 4×8, and partitions 646 having a size of 4×4.

In order to determine the at least one coded depth of the coding unitsconstituting the maximum coding unit 610, the coding unit determiner 120of the video encoding apparatus 100 performs encoding for coding unitscorresponding to each depth included in the maximum coding unit 610.

A number of deeper coding units according to depths including data inthe same range and the same size increases as the depth deepens. Forexample, four coding units corresponding to a depth of 2 are required tocover data that is included in one coding unit corresponding to a depthof 1. Accordingly, in order to compare encoding results of the same dataaccording to depths, the coding unit corresponding to the depth of 1 andfour coding units corresponding to the depth of 2 are each encoded.

In order to perform encoding for a current depth from among the depths,a least encoding error may be selected for the current depth byperforming encoding for each prediction unit in the coding unitscorresponding to the current depth, along the horizontal axis of thehierarchical structure 600. Alternatively, the minimum encoding errormay be searched for by comparing the least encoding errors according todepths, by performing encoding for each depth as the depth deepens alongthe vertical axis of the hierarchical structure 600. A depth and apartition having the minimum encoding error in the coding unit 610 maybe selected as the coded depth and a partition type of the coding unit610.

FIG. 15 is a diagram for describing a relationship between a coding unit710 and transformation units 720, according to an exemplary embodiment.

The video encoding apparatus 100 or the video decoding apparatus 200encodes or decodes an image according to coding units having sizessmaller than or equal to a maximum coding unit for each maximum codingunit. Sizes of transformation units for transformation during encodingmay be selected based on data units that are not larger than acorresponding coding unit.

For example, in the video encoding apparatus 100 or the video decodingapparatus 200, if a size of the coding unit 710 is 64×64, transformationmay be performed by using the transformation units 720 having a size of32×32.

Also, data of the coding unit 710 having the size of 64×64 may beencoded by performing the transformation on each of the transformationunits having the size of 32×32, 16×16, 8×8, and 4×4, which are smallerthan 64×64, and then a transformation unit having the least coding errormay be selected.

FIG. 16 is a diagram for describing encoding information of coding unitscorresponding to a coded depth, according to an exemplary embodiment.

The output unit 130 of the video encoding apparatus 100 may encode andtransmit information 800 about a partition type, information 810 about aprediction mode, and information 820 about a size of a transformationunit for each coding unit corresponding to a coded depth, as informationabout an encoding mode.

The information 800 indicates information about a shape of a partitionobtained by splitting a prediction unit of a current coding unit,wherein the partition is a data unit for prediction encoding the currentcoding unit. For example, a current coding unit CU_0 having a size of2N×2N may be split into any one of a partition 802 having a size of2N×2N, a partition 804 having a size of 2N×N, a partition 806 having asize of N×2N, and a partition 808 having a size of N×N. Here, theinformation 800 about a partition type is set to indicate one of thepartition 804 having a size of 2N×N, the partition 806 having a size ofN×2N, and the partition 808 having a size of N×N.

The information 810 indicates a prediction mode of each partition. Forexample, the information 810 may indicate a mode of prediction encodingperformed on a partition indicated by the information 800, i.e., anintra mode 812, an inter mode 814, or a skip mode 816.

The information 820 indicates a transformation unit to be based on whentransformation is performed on a current coding unit. For example, thetransformation unit may be a first intra transformation unit 822, asecond intra transformation unit 824, a first inter transformation unit826, or a second inter transformation unit 828.

The image data and encoding information extractor 220 of the videodecoding apparatus 200 may extract and use the information 800, 810, and820 for decoding, according to each deeper coding unit.

FIG. 17 is a diagram of deeper coding units according to depths,according to an exemplary embodiment.

Split information may be used to indicate a change of a depth. The spiltinformation indicates whether a coding unit of a current depth is splitinto coding units of a lower depth.

A prediction unit 910 for prediction encoding a coding unit 900 having adepth of 0 and a size of 2N_0×2N_0 may include partitions of a partitiontype 912 having a size of 2N_0×2N_0, a partition type 914 having a sizeof 2N_0×N_0, a partition type 916 having a size of N_0×2N_0, and apartition type 918 having a size of N_0×N_0. FIG. 17 only illustratesthe partition types 912 through 918 which are obtained by symmetricallysplitting the prediction unit 910, but a partition type is not limitedthereto, and the partitions of the prediction unit 910 may includeasymmetrical partitions, partitions having a predetermined shape, andpartitions having a geometrical shape.

Prediction encoding is repeatedly performed on one partition having asize of 2N_0×2N_0, two partitions having a size of 2N_0×N_0, twopartitions having a size of N_0×2N_0, and four partitions having a sizeof N_0×N_0, according to each partition type. The prediction encoding inan intra mode and an inter mode may be performed on the partitionshaving the sizes of 2N_0×2N_0, N_0×2N_0, 2N_0×N_0, and N_0×N_0. Theprediction encoding in a skip mode is performed only on the partitionhaving the size of 2N_0×2N_0.

If an encoding error is smallest in one of the partition types 912through 916, the prediction unit 910 may not be split into a lowerdepth.

If the encoding error is the smallest in the partition type 918, a depthis changed from 0 to 1 to split the partition type 918 in operation 920,and encoding is repeatedly performed on coding units 930 having a depthof 2 and a size of N_0×N_0 to search for a minimum encoding error.

A prediction unit 940 for prediction encoding the coding unit 930 havinga depth of 1 and a size of 2N_1×2N_1 (=N_0×N_0) may include partitionsof a partition type 942 having a size of 2N_1×2N_1, a partition type 944having a size of 2N_1×N_1, a partition type 946 having a size ofN_1×2N_1, and a partition type 948 having a size of N_1×N_1.

If an encoding error is the smallest in the partition type 948, a depthis changed from 1 to 2 to split the partition type 948 in operation 950,and encoding is repeatedly performed on coding units 960, which have adepth of 2 and a size of N_2×N_2 to search for a minimum encoding error.

When a maximum depth is d, split operation according to each depth maybe performed up to when a depth becomes d−1, and split information maybe encoded as up to when a depth is one of 0 to d−2. In other words,when encoding is performed up to when the depth is d−1 after a codingunit corresponding to a depth of d−2 is split in operation 970, aprediction unit 990 for prediction encoding a coding unit 980 having adepth of d−1 and a size of 2N_(d−1)×2N_(d−1) may include partitions of apartition type 992 having a size of 2N_(d−1)×2N_(d−1), a partition type994 having a size of 2N_(d−1)×N_(d−1), a partition type 996 having asize of N_(d−1)×2N_(d−1), and a partition type 998 having a size ofN_(d−1)×N_(d−1).

Prediction encoding may be repeatedly performed on one partition havinga size of 2N_(d−1)×2N_(d−1), two partitions having a size of2N_(d−1)×N_(d−1), two partitions having a size of N_(d−1)×2N_(d−1), fourpartitions having a size of N_(d−1)×N_(d−1) from among the partitiontypes 992 through 998 to search for a partition type having a minimumencoding error.

Even when the partition type 998 has the minimum encoding error, since amaximum depth is d, a coding unit CU_(d−1) having a depth of d−1 is nolonger split to a lower depth, and a coded depth for the coding unitsconstituting a current maximum coding unit 900 is determined to be d−1and a partition type of the current maximum coding unit 900 may bedetermined to be N_(d−1)×N_(d−1). Also, since the maximum depth is d anda minimum coding unit 980 having a lowermost depth of d−1 is no longersplit to a lower depth, split information for the minimum coding unit980 is not set.

A data unit 999 may be a ‘minimum unit’ for the current maximum codingunit. A minimum unit according to an exemplary embodiment may be asquare data unit obtained by splitting a minimum coding unit 980 by 4.By performing the encoding repeatedly, the video encoding apparatus 100may select a depth having the least encoding error by comparing encodingerrors according to depths of the coding unit 900 to determine a codeddepth, and set a corresponding partition type and a prediction mode asan encoding mode of the coded depth.

As such, the minimum encoding errors according to depths are compared inall of the depths of 1 through d, and a depth having the least encodingerror may be determined as a coded depth. The coded depth, the partitiontype of the prediction unit, and the prediction mode may be encoded andtransmitted as information about an encoding mode. Also, since a codingunit is split from a depth of 0 to a coded depth, only split informationof the coded depth is set to 0, and split information of depthsexcluding the coded depth is set to 1.

The image data and encoding information extractor 220 of the videodecoding apparatus 200 may extract and use the information about thecoded depth and the prediction unit of the coding unit 900 to decode thepartition type 912. The video decoding apparatus 200 may determine adepth, in which split information is 0, as a coded depth by using splitinformation according to depths, and use information about an encodingmode of the corresponding depth for decoding.

FIGS. 18 through 20 are diagrams for describing a relationship betweencoding units 1010, prediction units 1060, and transformation units 1070,according to an exemplary embodiment.

The coding units 1010 are coding units having a tree structure,corresponding to coded depths determined by the video encoding apparatus100, in a maximum coding unit. The prediction units 1060 are partitionsof prediction units of each of the coding units 1010, and thetransformation units 1070 are transformation units of each of the codingunits 1010.

When a depth of a maximum coding unit is 0 in the coding units 1010,depths of coding units 1012 and 1054 are 1, depths of coding units 1014,1016, 1018, 1028, 1050, and 1052 are 2, depths of coding units 1020,1022, 1024, 1026, 1030, 1032, and 1048 are 3, and depths of coding units1040, 1042, 1044, and 1046 are 4.

In the prediction units 1060, some encoding units 1014, 1016, 1022,1032, 1048, 1050, 1052, and 1054 are obtained by splitting the codingunits in the encoding units 1010. In other words, partition types in thecoding units 1014, 1022, 1050, and 1054 have a size of 2N×N, partitiontypes in the coding units 1016, 1048, and 1052 have a size of N×2N, anda partition type of the coding unit 1032 has a size of N×N. Predictionunits and partitions of the coding units 1010 are smaller than or equalto each coding unit.

Transformation or inverse transformation is performed on image data ofthe coding unit 1052 in the transformation units 1070 in a data unitthat is smaller than the coding unit 1052. Also, the coding units 1014,1016, 1022, 1032, 1048, 1050, and 1052 in the transformation units 1070are different from those in the prediction units 1060 in terms of sizesand shapes. In other words, the video encoding and decoding apparatuses100 and 200 may perform intra prediction, motion estimation, motioncompensation, transformation, and inverse transformation individually ona data unit in the same coding unit.

Accordingly, encoding is recursively performed on each of coding unitshaving a hierarchical structure in each region of a maximum coding unitto determine an optimum coding unit, and thus coding units having arecursive tree structure may be obtained. Encoding information mayinclude split information about a coding unit, information about apartition type, information about a prediction mode, and informationabout a size of a transformation unit. Table 1 shows the encodinginformation that may be set by the video encoding and decodingapparatuses 100 and 200.

TABLE 1 Split Information 0 Split (Encoding on Coding Unit having Sizeof 2N × 2N and Current Depth of d) Information 1 Prediction PartitionType Size of Transformation Unit Repeatedly Mode Encode Coding IntraSymmetrical Asymmetrical Split Split Units having Inter PartitionPartition Type Information 0 of Information 1 of Lower Depth Skip (OnlyType Transformation Transformation of d + 1 2N × 2N) Unit Unit 2N × 2N2N × nU 2N × 2N N × N 2N × N  2N × nD (Symmetrical  N × 2N nL × 2N Type)N × N nR × 2N N/2 × N/2 (Asymmetrical Type)

The output unit 130 of the video encoding apparatus 100 may output theencoding information about the coding units having a tree structure, andthe image data and encoding information extractor 220 of the videodecoding apparatus 200 may extract the encoding information about thecoding units having a tree structure from a received bitstream.

Split information indicates whether a current coding unit is split intocoding units of a lower depth. If split information of a current depth dis 0, a depth, in which a current coding unit is no longer split into alower depth, is a coded depth, and thus information about a partitiontype, prediction mode, and a size of a transformation unit may bedefined for the coded depth. If the current coding unit is further splitaccording to the split information, encoding is independently performedon four split coding units of a lower depth.

A prediction mode may be one of an intra mode, an inter mode, and a skipmode. The intra mode and the inter mode may be defined in all partitiontypes, and the skip mode is defined only in a partition type having asize of 2N×2N.

The information about the partition type may indicate symmetricalpartition types having sizes of 2N×2N, 2N×N, N×2N, and N×N, which areobtained by symmetrically splitting a height or a width of a predictionunit, and asymmetrical partition types having sizes of 2N×nU, 2N×nD,nL×2N, and nR×2N, which are obtained by asymmetrically splitting theheight or width of the prediction unit. The asymmetrical partition typeshaving the sizes of 2N×nU and 2N×nD may be respectively obtained bysplitting the height of the prediction unit in 1:3 and 3:1, and theasymmetrical partition types having the sizes of nL×2N and nR×2N may berespectively obtained by splitting the width of the prediction unit in1:3 and 3:1

The size of the transformation unit may be set to be two types in theintra mode and two types in the inter mode. In other words, if splitinformation of the transformation unit is 0, the size of thetransformation unit may be 2N×2N, which is the size of the currentcoding unit. If split information of the transformation unit is 1, thetransformation units may be obtained by splitting the current codingunit. Also, if a partition type of the current coding unit having thesize of 2N×2N is a symmetrical partition type, a size of atransformation unit may be N×N, and if the partition type of the currentcoding unit is an asymmetrical partition type, the size of thetransformation unit may be N/2×N/2.

The encoding information about coding units having a tree structure mayinclude at least one of a coding unit corresponding to a coded depth, aprediction unit, and a minimum unit. The coding unit corresponding tothe coded depth may include at least one of a prediction unit and aminimum unit containing the same encoding information.

Accordingly, it is determined whether adjacent data units are includedin the same coding unit corresponding to the coded depth by comparingencoding information of the adjacent data units. Also, a correspondingcoding unit corresponding to a coded depth is determined by usingencoding information of a data unit, and thus a distribution of codeddepths in a maximum coding unit may be determined.

Accordingly, if a current coding unit is predicted based on encodinginformation of adjacent data units, encoding information of data unitsin deeper coding units adjacent to the current coding unit may bedirectly referred to and used.

Alternatively, if a current coding unit is predicted based on encodinginformation of adjacent data units, data units adjacent to the currentcoding unit are searched using encoded information of the data units,and the searched adjacent coding units may be referred for predictingthe current coding unit.

FIG. 21 is a diagram for describing a relationship between a codingunit, a prediction unit, and a transformation unit, according toencoding mode information of Table 1.

A maximum coding unit 1300 includes coding units 1302, 1304, 1306, 1312,1314, 1316, and 1318 of coded depths. Here, since the coding unit 1318is a coding unit of a coded depth, split information may be set to 0.Information about a partition type of the coding unit 1318 having a sizeof 2N×2N may be set to be one of a partition type 1322 having a size of2N×2N, a partition type 1324 having a size of 2N×N, a partition type1326 having a size of N×2N, a partition type 1328 having a size of N×N,a partition type 1332 having a size of 2N×nU, a partition type 1334having a size of 2N×nD, a partition type 1336 having a size of nL×2N,and a partition type 1338 having a size of nR×2N.

Split information (TU size flag) of a transformation unit is a type of atransformation index. The size of the transformation unit correspondingto the transformation index may be changed according to a predictionunit type or partition type of the coding unit.

For example, when the partition type is set to be symmetrical, i.e., thepartition type 1322, 1324, 1326, or 1328, a transformation unit 1342having a size of 2N×2N is set if a TU size flag of a transformation unitis 0, and a transformation unit 1344 having a size of N×N is set if a TUsize flag is 1.

When the partition type is set to be asymmetrical, i.e., the partitiontype 1332, 1334, 1336, or 1338, a transformation unit 1352 having a sizeof 2N×2N is set if a TU size flag is 0, and a transformation unit 1354having a size of N/2×N/2 is set if a TU size flag is 1.

Referring to FIG. 21, the TU size flag is a flag having a value or 0 or1, but the TU size flag is not limited to 1 bit, and a transformationunit may be hierarchically split having a tree structure while the TUsize flag increases from 0. Split information (TU size flag) of atransformation unit may be an example of a transformation index.

In this case, the size of a transformation unit that has been actuallyused may be expressed by using a TU size flag of a transformation unit,according to an exemplary embodiment, together with a maximum size andminimum size of the transformation unit. The video encoding apparatus100 is capable of encoding maximum transformation unit size information,minimum transformation unit size information, and a maximum TU sizeflag. The result of encoding the maximum transformation unit sizeinformation, the minimum transformation unit size information, and themaximum TU size flag may be inserted into an SPS. The video decodingapparatus 200 may decode video by using the maximum transformation unitsize information, the minimum transformation unit size information, andthe maximum TU size flag.

For example, (a) if the size of a current coding unit is 64×64 and amaximum transformation unit size is 32×32, (a−1) then the size of atransformation unit may be 32×32 when a TU size flag is 0, (a−2) may be16×16 when the TU size flag is 1, and (a−3) may be 8×8 when the TU sizeflag is 2.

As another example, (b) if the size of the current coding unit is 32×32and a minimum transformation unit size is 32×32, (b−1) then the size ofthe transformation unit may be 32×32 when the TU size flag is 0. Here,the TU size flag cannot be set to a value other than 0, since the sizeof the transformation unit cannot be less than 32×32.

As another example, (c) if the size of the current coding unit is 64×64and a maximum TU size flag is 1, then the TU size flag may be 0 or 1.Here, the TU size flag cannot be set to a value other than 0 or 1.

Thus, if it is defined that the maximum TU size flag is‘MaxTransformSizeIndex’, a minimum transformation unit size is‘MinTransformSize’, and a transformation unit size is ‘RootTuSize’ whenthe TU size flag is 0, then a current minimum transformation unit size‘CurrMinTuSize’ that can be determined in a current coding unit, may bedefined by Equation (1):

CurrMinTuSize=max(MinTransformSize, RootTuSize/(2̂MaxTransformSizeIndex))  (1)

Compared to the current minimum transformation unit size ‘CurrMinTuSize’that can be determined in the current coding unit, a transformation unitsize ‘RootTuSize’ when the TU size flag is 0 may denote a maximumtransformation unit size that can be selected in the system. In Equation(1), ‘RootTuSize/(2̂MaxTransformSizeIndex)’ denotes a transformation unitsize when the transformation unit size ‘RootTuSize’, when the TU sizeflag is 0, is split a number of times corresponding to the maximum TUsize flag, and ‘MinTransformSize’ denotes a minimum transformation size.Thus, a smaller value from among ‘RootTuSize/(2̂MaxTransformSizeIndex)’and ‘MinTransformSize’ may be the current minimum transformation unitsize ‘CurrMinTuSize’ that can be determined in the current coding unit.

According to an exemplary embodiment, the maximum transformation unitsize RootTuSize may vary according to the type of a prediction mode.

For example, if a current prediction mode is an inter mode, then‘RootTuSize’ may be determined by using Equation (2) below. In Equation(2), ‘MaxTransformSize’ denotes a maximum transformation unit size, and‘PUSize’ denotes a current prediction unit size.

RootTuSize=min(MaxTransformSize, PUSize)   (2)

That is, if the current prediction mode is the inter mode, thetransformation unit size ‘RootTuSize’, when the TU size flag is 0, maybe a smaller value from among the maximum transformation unit size andthe current prediction unit size.

If a prediction mode of a current partition unit is an intra mode,‘RootTuSize’ may be determined by using Equation (3) below. In Equation(3), ‘PartitionSize’ denotes the size of the current partition unit.

RootTuSize=min(MaxTransformSize, PartitionSize)   (3)

That is, if the current prediction mode is the intra mode, thetransformation unit size ‘RootTuSize’ when the TU size flag is 0 may bea smaller value from among the maximum transformation unit size and thesize of the current partition unit.

However, the current maximum transformation unit size ‘RootTuSize’ thatvaries according to the type of a prediction mode in a partition unit isjust an example and one or more other exemplary embodiments are notlimited thereto.

According to the video encoding method based on coding units having atree structure as described with reference to FIGS. 9 through 21, imagedata of a spatial region is encoded for each coding unit of a treestructure. According to the video decoding method based on coding unitshaving a tree structure, decoding is performed for each maximum codingunit to restore image data of a spatial region. Thus, a picture and avideo that is a picture sequence may be restored. The restored video maybe reproduced by a reproducing apparatus, stored in a storage medium, ortransmitted through a network.

It is understood that one or more exemplary embodiments may be writtenas computer programs and may be implemented in general-use digitalcomputers that execute the programs using a computer-readable recordingmedium. Examples of the computer-readable recording medium includemagnetic storage media (e.g., ROM, floppy discs, hard discs, etc.) andoptical recording media (e.g., CD-ROMs, or DVDs).

For convenience of description, the video encoding method according tothe motion vector prediction method described with reference to FIGS. 1through 21, will be collectively referred to as a ‘video encoding methodaccording to the present disclosure’. In addition, the video decodingmethod according to the motion vector prediction method described withreference to FIGS. 1 through 21, will be referred to as a ‘videodecoding method according to the present disclosure’.

Also, a video encoding apparatus including the inter predictionapparatus 20, the video encoder 70, the video decoder 80, the videoencoding apparatus 100, or the image encoder 400, which has beendescribed with reference to FIGS. 1 through 21, will be referred to as a‘video encoding apparatus according to the present disclosure’. Inaddition, a video decoding apparatus including the inter predictionapparatus 20, the video decoder 80, the video decoding apparatus 200, orthe image decoder 500, which has been described with reference to FIGS.1 through 21, will be referred to as a ‘video decoding apparatusaccording to the present disclosure’.

A computer-readable recording medium storing a program, e.g., a disc26000, according to one or more exemplary embodiments will now bedescribed in detail.

FIG. 22 is a diagram of a physical structure of the disc 26000 in whicha program is stored, according to an exemplary embodiment. The disc26000, which is a storage medium, may be a hard drive, a compactdisc-read only memory (CD-ROM) disc, a Blu-ray disc, a digital versatiledisc (DVD), etc. The disc 26000 includes a plurality of concentrictracks Tr that are each divided into a specific number of sectors Se ina circumferential direction of the disc 26000. In a specific region ofthe disc 26000, a program that executes the quantization parameterdetermining method, the video encoding method, and the video decodingmethod described above may be assigned and stored.

A computer system embodied using a storage medium that stores a programfor executing the video encoding method and the video decoding method asdescribed above will now be described with reference to FIG. 23.

FIG. 23 is a diagram of a disc drive 26800 for recording and reading aprogram by using the disc 26000. A computer system 26700 may store aprogram that executes at least one of a video encoding method and avideo decoding method according to exemplary embodiments, in the disc26000 via the disc drive 26800. To run the program stored in the disc26000 in the computer system 26700, the program may be read from thedisc 26000 and be transmitted to the computer system 26700 by using thedisc drive 26800.

The program that executes at least one of a video encoding method and avideo decoding method according to exemplary embodiments may be storednot only in the disc 26000 illustrated in FIG. 22 or 23 but also in amemory card, a ROM cassette, or a solid state drive (SSD).

A system to which the video encoding method and a video decoding methoddescribed above are applied will be described below.

FIG. 24 is a diagram of an overall structure of a content supply system11000 for providing a content distribution service, according to anexemplary embodiment. A service area of a communication system isdivided into predetermined-sized cells, and wireless base stations11700, 11800, 11900, and 12000 are installed in these cells,respectively.

The content supply system 11000 includes a plurality of independentdevices. For example, the plurality of independent devices, such as acomputer 12100, a personal digital assistant (PDA) 12200, a video camera12300, and a mobile phone 12500, are connected to the Internet 11100 viaan internet service provider 11200, a communication network 11400, andthe wireless base stations 11700, 11800, 11900, and 12000.

However, the content supply system 11000 is not limited to asillustrated in FIG. 24 and devices may be selectively connected theretoin one or more other exemplary embodiments. The plurality of independentdevices may be directly connected to the communication network 11400,not via the wireless base stations 11700, 11800, 11900, and 12000.

The video camera 12300 is an imaging device, e.g., a digital videocamera, which is capable of capturing video images. The mobile phone12500 may employ at least one communication method from among variousprotocols, e.g., Personal Digital Communications (PDC), Code DivisionMultiple Access (CDMA), Wideband-Code Division Multiple Access (W-CDMA),Global System for Mobile Communications (GSM), and Personal HandyphoneSystem (PHS).

The video camera 12300 may be connected to a streaming server 11300 viathe wireless base station 11900 and the communication network 11400. Thestreaming server 11300 allows content received from a user via the videocamera 12300 to be streamed via a real-time broadcast. The contentreceived from the video camera 12300 may be encoded using the videocamera 12300 or the streaming server 11300. Video data captured by thevideo camera 12300 may be transmitted to the streaming server 11300 viathe computer 12100.

Video data captured by a camera 12600 may also be transmitted to thestreaming server 11300 via the computer 12100. The camera 12600 is animaging device capable of capturing both still images and video images,similar to a digital camera. The video data captured by the camera 12600may be encoded using the camera 12600 or the computer 12100. Softwarethat performs encoding and decoding video may be stored in acomputer-readable recording medium, e.g., a CD-ROM disc, a floppy disc,a hard disc drive, an SSD, or a memory card, which may be accessible bythe computer 12100.

If video data is captured by a camera built in the mobile phone 12500,the video data may be received from the mobile phone 12500.

The video data may also be encoded by a large scale integrated circuit(LSI) system installed in the video camera 12300, the mobile phone12500, or the camera 12600.

The content supply system 11000 may encode content data recorded by auser using the video camera 12300, the camera 12600, the mobile phone12500, or another imaging device, e.g., content recorded during aconcert, and transmit the encoded content data to the streaming server11300. The streaming server 11300 may transmit the encoded content datain a type of a streaming content to other clients that request thecontent data.

The clients are devices capable of decoding the encoded content data,e.g., the computer 12100, the PDA 12200, the video camera 12300, or themobile phone 12500. Thus, the content supply system 11000 allows theclients to receive and reproduce the encoded content data. Also, thecontent supply system 11000 allows the clients to receive the encodedcontent data and decode and reproduce the encoded content data in realtime, thereby enabling personal broadcasting.

Encoding and decoding operations of the plurality of independent devicesincluded in the content supply system 11000 may be similar to those of avideo encoding apparatus and a video decoding apparatus according to oneor more exemplary embodiments described above.

The mobile phone 12500 included in the content supply system 11000according to an exemplary embodiment will now be described in greaterdetail with reference to FIGS. 25 and 26.

FIG. 25 illustrates an external structure of the mobile phone 12500 towhich a video encoding method and a video decoding method are applied,according to an exemplary embodiment. The mobile phone 12500 may be asmart phone, the functions of which are not limited and a large numberof the functions of which may be changed or expanded.

The mobile phone 12500 includes an internal antenna 12510 via which aradio-frequency (RF) signal may be exchanged with the wireless basestation 12000 of FIG. 21, and includes a display screen 12520 fordisplaying images captured by a camera 12530 or images that are receivedvia the antenna 12510 and decoded, e.g., a liquid crystal display (LCD)or an organic light-emitting diode (OLED) screen. The mobile phone 12500includes an operation panel 12540 including a control button and a touchpanel. If the display screen 12520 is a touch screen, the operationpanel 12540 further includes a touch sensing panel of the display screen12520. The mobile phone 12500 includes a speaker 12580 for outputtingvoice and sound or another type of sound output unit, and a microphone12550 for inputting voice and sound or another type sound input unit.The mobile phone 12500 further includes the camera 12530, such as acharge-coupled device (CCD) camera, to capture video and still images.The mobile phone 12500 may further include: a storage medium 12570 forstoring encoded/decoded data, e.g., video or still images captured bythe camera 12530, received via email, or obtained according to variousways; and a slot 12560 via which the storage medium 12570 is loaded intothe mobile phone 12500. The storage medium 12570 may be a flash memory,e.g., a secure digital (SD) card or an electrically erasable andprogrammable read only memory (EEPROM) included in a plastic case,although it is understood that one or more other exemplary embodimentsare not limited thereto.

FIG. 26 illustrates an internal structure of the mobile phone 12500,according to an exemplary embodiment. To systemically control parts ofthe mobile phone 12500 including the display screen 12520 and theoperation panel 12540, a power supply circuit 12700, an operation inputcontroller 12640, an image encoding unit 12720, a camera interface12630, an LCD controller 12620, an image decoding unit 12690 (e.g.,image decoder), a multiplexer/demultiplexer 12680, a recording/readingunit 12670 (e.g., recorder/reader), a modulation/demodulation unit 12660(e.g., modulator/demodulator), and a sound processor 12650 are connectedto a central controller 12710 via a synchronization bus 12730.

If a user operates a power button and sets from a ‘power off’ state to apower on’ state, the power supply circuit 12700 supplies power to allthe parts of the mobile phone 12500 from a battery pack, thereby settingthe mobile phone 12500 in an operation mode.

The central controller 12710 includes a central processing unit (CPU), aROM, and a RAM.

While the mobile phone 12500 transmits communication data to theoutside, a digital signal is generated by the mobile phone 12500 undercontrol of the central controller 12710. For example, the soundprocessor 12650 may generate a digital sound signal, the image encodingunit 12720 may generate a digital image signal, and text data of amessage may be generated via the operation panel 12540 and the operationinput controller 12640. When a digital signal is transmitted to themodulation/demodulation unit 12660 under control of the centralcontroller 12710, the modulation/demodulation unit 12660 modulates afrequency band of the digital signal, and a communication circuit 12610performs digital-to-analog conversion (DAC) and frequency conversion onthe frequency band-modulated digital sound signal. A transmission signaloutput from the communication circuit 12610 may be transmitted to avoice communication base station or the wireless base station 12000 viathe antenna 12510.

For example, when the mobile phone 12500 is in a conversation mode, asound signal obtained via the microphone 12550 is transformed into adigital sound signal by the sound processor 12650, under control of thecentral controller 12710. The digital sound signal may be transformedinto a transformation signal via the modulation/demodulation unit 12660and the communication circuit 12610, and may be transmitted via theantenna 12510.

When a text message, e.g., short message service message, email, etc.,is transmitted in a data communication mode, text data of the textmessage is input via the operation panel 12540 and is transmitted to thecentral controller 12710 via the operation input controller 12640. Undercontrol of the central controller 12710, the text data is transformedinto a transmission signal via the modulation/demodulation unit 12660and the communication circuit 12610 and is transmitted to the wirelessbase station 12000 via the antenna 12510.

To transmit image data in the data communication mode, image datacaptured by the camera 12530 is provided to the image encoding unit12720 via the camera interface 12630. The captured image data may bedirectly displayed on the display screen 12520 via the camera interface12630 and the LCD controller 12620.

A structure of the image encoding unit 12720 may correspond to that ofthe video encoding apparatus 100 described above. The image encodingunit 12720 may transform the image data received from the camera 12530into compressed and encoded image data according to the video encodingmethod described above, and then output the encoded image data to themultiplexer/demultiplexer 12680. During a recording operation of thecamera 12530, a sound signal obtained by the microphone 12550 of themobile phone 12500 may be transformed into digital sound data via thesound processor 12650, and the digital sound data may be transmitted tothe multiplexer/demultiplexer 12680.

The multiplexer/demultiplexer 12680 multiplexes the encoded image datareceived from the image encoding unit 12720, together with the sounddata received from the sound processor 12650. A result of multiplexingthe data may be transformed into a transmission signal via themodulation/demodulation unit 12660 and the communication circuit 12610,and may then be transmitted via the antenna 12510.

While the mobile phone 12500 receives communication data from theoutside, frequency recovery and ADC are performed on a signal receivedvia the antenna 12510 to transform the signal into a digital signal. Themodulation/demodulation unit 12660 modulates a frequency band of thedigital signal. The frequency-band modulated digital signal istransmitted to the video decoding unit 12690, the sound processor 12650,or the LCD controller 12620, according to the type of the digitalsignal.

In the conversation mode, the mobile phone 12500 amplifies a signalreceived via the antenna 12510, and obtains a digital sound signal byperforming frequency conversion and ADC on the amplified signal. Areceived digital sound signal is transformed into an analog sound signalvia the modulation/demodulation unit 12660 and the sound processor12650, and the analog sound signal is output via the speaker 12580,under control of the central controller 12710.

When in the data communication mode, data of a video file accessed at anInternet website is received, a signal received from the wireless basestation 12000 via the antenna 12510 is output as multiplexed data viathe modulation/demodulation unit 12660, and the multiplexed data istransmitted to the multiplexer/demultiplexer 12680.

To decode the multiplexed data received via the antenna 12510, themultiplexer/demultiplexer 12680 demultiplexes the multiplexed data intoan encoded video data stream and an encoded audio data stream. Via thesynchronization bus 12730, the encoded video data stream and the encodedaudio data stream are provided to the video decoding unit 12690 and thesound processor 12650, respectively.

A structure of the image decoding unit 12690 may correspond to that ofthe video decoding apparatus 200 described above. The image decodingunit 12690 may decode the encoded video data to obtain restored videodata and provide the restored video data to the display screen 12520 viathe LCD controller 12620, according to the video decoding methoddescribed above.

Thus, the data of the video file accessed at the Internet website may bedisplayed on the display screen 12520. At the same time, the soundprocessor 12650 may transform audio data into an analog sound signal,and provide the analog sound signal to the speaker 12580. Thus, audiodata contained in the video file accessed at the Internet website mayalso be reproduced via the speaker 12580.

The mobile phone 12500 or another type of communication terminal may bea transceiving terminal including both a video encoding apparatus and avideo decoding apparatus according to one or more exemplary embodiments,may be a transceiving terminal including only the video encodingapparatus, or may be a transceiving terminal including only the videodecoding apparatus.

A communication system according to an exemplary embodiment is notlimited to the communication system described above with reference toFIG. 24. For example, FIG. 27 illustrates a digital broadcasting systememploying a communication system, according to an exemplary embodiment.The digital broadcasting system of FIG. 27 may receive a digitalbroadcast transmitted via a satellite or a terrestrial network by usinga video encoding apparatus and a video decoding apparatus according toone or more exemplary embodiments.

Specifically, a broadcasting station 12890 transmits a video data streamto a communication satellite or a broadcasting satellite 12900 by usingradio waves. The broadcasting satellite 12900 transmits a broadcastsignal, and the broadcast signal is transmitted to a satellite broadcastreceiver via a household antenna 12860. In every house, an encoded videostream may be decoded and reproduced by a TV receiver 12810, a set-topbox 12870, or another device.

When a video decoding apparatus according to an exemplary embodiment isimplemented in a reproducing apparatus 12830, the reproducing apparatus12830 may parse and decode an encoded video stream recorded on a storagemedium 12820, such as a disc or a memory card to restore digitalsignals. Thus, the restored video signal may be reproduced, for example,on a monitor 12840.

In the set-top box 12870 connected to the antenna 12860 for asatellite/terrestrial broadcast or a cable antenna 12850 for receiving acable television (TV) broadcast, a video decoding apparatus according toexemplary embodiments may be installed. Data output from the set-top box12870 may also be reproduced on a TV monitor 12880.

As another example, a video decoding apparatus according to an exemplaryembodiment may be installed in the TV receiver 12810 instead of theset-top box 12870.

An automobile 12920 that has an appropriate antenna 12910 may receive asignal transmitted from the satellite 12900 or the wireless base station11700 of FIG. 21. A decoded video may be reproduced on a display screenof an automobile navigation system 12930 installed in the automobile12920.

A video signal may be encoded by a video encoding apparatus according toan exemplary embodiment and may then be stored in a storage medium.Specifically, an image signal may be stored in a DVD disc 12960 by a DVDrecorder or may be stored in a hard disc by a hard disc recorder 12950.As another example, the video signal may be stored in an SD card 12970.If the hard disc recorder 12950 includes a video decoding apparatusaccording to an exemplary embodiment, a video signal recorded on the DVDdisc 12960, the SD card 12970, or another storage medium may bereproduced on the TV monitor 12880.

The automobile navigation system 12930 may not include the camera 12530,the camera interface 12630, and the image encoding unit 12720 of FIG.24. For example, the computer 12100 and the TV receiver 12810 may not beincluded in the camera 12530, the camera interface 12630, and the imageencoding unit 12720 of FIG. 24.

FIG. 28 is a diagram illustrating a network structure of a cloudcomputing system using a video encoding apparatus and a video decodingapparatus, according to an exemplary embodiment.

The cloud computing system may include a cloud computing server 14000, auser database (DB) 14100, a plurality of computing resources 14200, anda user terminal.

The cloud computing system provides an on-demand outsourcing service ofthe plurality of computing resources 14200 via a data communicationnetwork, e.g., the Internet, in response to a request from the userterminal. Under a cloud computing environment, a service providerprovides users with desired services by combining computing resources atdata centers located at physically different locations by usingvirtualization technology. A service user does not have to installcomputing resources, e.g., an application, a storage, an operatingsystem (OS), and security, into his/her own terminal in order to usethem, but may select and use desired services from among services in avirtual space generated through the virtualization technology, at adesired point in time.

A user terminal of a specified service user is connected to the cloudcomputing server 14000 via a data communication network including theInternet and a mobile telecommunication network. User terminals may beprovided cloud computing services, and particularly video reproductionservices, from the cloud computing server 14000. The user terminals maybe various types of electronic devices capable of being connected to theInternet, e.g., a desktop PC 14300, a smart TV 14400, a smart phone14500, a notebook computer 14600, a portable multimedia player (PMP)14700, a tablet PC 14800, and the like.

The cloud computing server 14000 may combine the plurality of computingresources 14200 distributed in a cloud network and provide userterminals with a result of combining. The plurality of computingresources 14200 may include various data services, and may include datauploaded from user terminals. As described above, the cloud computingserver 14000 may provide user terminals with desired services bycombining video database distributed in different regions according tothe virtualization technology.

User information about users who have subscribed for a cloud computingservice is stored in the user DB 14100. The user information may includelogging information, addresses, names, personal credit information,etc., of the users. The user information may further include indexes ofvideos. Here, the indexes may include a list of videos that have alreadybeen reproduced, a list of videos that are being reproduced, a pausingpoint of a video that was being reproduced, and the like.

Information about a video stored in the user DB 14100 may be sharedbetween user devices. For example, when a video service is provided tothe notebook computer 14600 in response to a request from the notebookcomputer 14600, a reproduction history of the video service is stored inthe user DB 14100. When a request to reproduce this video service isreceived from the smart phone 14500, the cloud computing server 14000searches for and reproduces this video service, based on the user DB14100. When the smart phone 14500 receives a video data stream from thecloud computing server 14000, operations of reproducing video bydecoding the video data stream are similar to operations of the mobilephone 12500 described above with reference to FIG. 21.

The cloud computing server 14000 may refer to a reproduction history ofa desired video service, stored in the user DB 14100. For example, thecloud computing server 14000 receives a request to reproduce a videostored in the user DB 14100, from a user terminal. If this video wasbeing reproduced, then a method of streaming this video, performed bythe cloud computing server 14000, may vary according to the request fromthe user terminal, i.e., according to whether the video will bereproduced, starting from a start thereof or a pausing point thereof.For example, if the user terminal requests to reproduce the video,starting from the start thereof, the cloud computing server 14000transmits streaming data of the video starting from a first framethereof to the user terminal. If the user terminal requests to reproducethe video, starting from the pausing point thereof, the cloud computingserver 14000 transmits streaming data of the video starting from a framecorresponding to the pausing point, to the user terminal.

In this case, the user terminal may include a video decoding apparatusas described above with reference to FIGS. 1 to 23. As another example,the user terminal may include a video encoding apparatus as describedabove with reference to FIGS. 1 to 23. Alternatively, the user terminalmay include both the video decoding apparatus and the video encodingapparatus as described above with reference to FIGS. 1 to 23.

Various applications of a video encoding method, a video decodingmethod, a video encoding apparatus, and a video decoding apparatusaccording to exemplary embodiments described above with reference toFIGS. 1 to 23 have been described above with reference to FIGS. 22 to28. However, methods of storing the video encoding method and the videodecoding method in a storage medium or methods of implementing the videoencoding apparatus and the video decoding apparatus in a device,according to various exemplary embodiments, are not limited to theexemplary embodiments described above with reference to FIGS. 22 to 28.

While exemplary embodiments have been particularly shown and describedabove, it will be understood by those of ordinary skill in the art thatvarious changes in form and details may be made therein withoutdeparting from the spirit and scope according to the present disclosureas defined by the following claims.

1. An apparatus for decoding an image, the apparatus comprising: atleast one processor configure to: determine a collocated picture fromamong pictures restored before a current picture according to acollocated index; parse information about a long-term reference picturefrom a bitstream; when one of a reference picture of a collocated blockincluded in the collocated picture and a reference picture of a currentblock is determined as a long-term reference picture, and the other oneof the reference picture of the collocated block and the referencepicture of the current block is determined as a short-term referencepicture based on the information about the long-term reference picture,determine that a motion vector of the collocated block is un-availableso that the motion vector of the collocated block is not used to predicta motion vector of the current block; when both of the reference pictureof the collocated block and the reference picture of the current blockare determined as long-term reference pictures based on the informationabout the long-term reference picture, obtain a temporal motion vectorprediction candidate without scaling the motion vector of the collocatedblock; receive prediction information of a candidate block as predictioninformation of the current block that indicates the candidate block usedto derive a motion vector predictor of the current block; determine themotion vector predictor of the current block from among motion vectorprediction candidates, comprising the temporal motion vector predictioncandidate, based on the prediction information of the candidate block;and generate the motion vector of the current block using the motionvector predictor, wherein the scaling is based on a ratio of a distance(Td) between the collocated picture and the reference picture of thecollocated block and a distance (Tb) between the current picture and thereference picture of the current block.
 2. An apparatus for encoding animage, the apparatus comprising: at least one processor configure to:generate a collocated index for determining a collocated picture fromamong pictures restored before a current picture; when one of areference picture of a collocated block included in the collocatedpicture and a reference picture of a current block is determined as along-term reference picture, and the other one of the reference pictureof the collocated block and the reference picture of the current blockis determined as a short-term reference picture, determine that a motionvector of the collocated block is un-available so that the motion vectorof the collocated block is not used to predict a motion vector of thecurrent block; when both of the reference picture of the collocatedblock and the reference picture of the current block are determined aslong-term reference pictures, obtain a temporal motion vector predictioncandidate without scaling the motion vector of the collocated block;generate information about a long-term reference picture for determiningwhether the reference picture of the current block is the long-termreference picture; determine a motion vector predictor of the currentblock from among motion vector prediction candidates, comprising thetemporal motion vector prediction candidate; and generate predictioninformation of a candidate block as prediction information of thecurrent block that indicates the candidate block used to derive themotion vector predictor of the current block, wherein the scaling isbased on a ratio of a distance (Td) between the collocated picture andthe reference picture of the collocated block and a distance (Tb)between the current picture and the reference picture of the currentblock.
 3. A method for encoding an image, the method comprising:generating a collocated index for determining a collocated picture fromamong pictures restored before a current picture; when one of areference picture of a collocated block included in the collocatedpicture and a reference picture of a current block is determined as along-term reference picture, and the other one of the reference pictureof the collocated block and the reference picture of the current blockis determined as a short-term reference picture, determining that amotion vector of the collocated block is un-available so that the motionvector of the collocated block is not used to predict a motion vector ofthe current block; when both of the reference picture of the collocatedblock and the reference picture of the current block are determined aslong-term reference pictures, obtaining a temporal motion vectorprediction candidate without scaling the motion vector of the collocatedblock; generating information about a long-term reference picture fordetermining whether the reference picture of the current block is thelong-term reference picture; determining a motion vector predictor ofthe current block from among motion vector prediction candidates,comprising the temporal motion vector prediction candidate; andgenerating prediction information of a candidate block as predictioninformation of the current block that indicates the candidate block usedto derive the motion vector predictor of the current block, wherein thescaling is based on a ratio of a distance (Td) between the collocatedpicture and the reference picture of the collocated block and a distance(Tb) between the current picture and the reference picture of thecurrent block.
 4. A non-transitory computer-readable storage mediumstoring a bitstream generated by at least one processor, the bitstreamcomprising: a collocated index for determining a collocated picture fromamong pictures restored before a current picture; information about along-term reference picture for determining whether a reference pictureof a current block is a long-term reference picture; and predictioninformation of a candidate block as prediction information of thecurrent block that indicates the candidate block used to derive a motionvector predictor of the current block, wherein when one of a referencepicture of a collocated block included in the collocated picture and thereference picture of a current block is determined as the long-termreference picture, and the other one of the reference picture of thecollocated block and the reference picture of the current block isdetermined as a short-term reference picture, a motion vector of thecollocated block is determined as un-available so that the motion vectorof the collocated block is not used to predict the motion vector of thecurrent block; when both of the reference picture of the collocatedblock and the reference picture of the current block are determined aslong-term reference pictures, a temporal motion vector predictioncandidate is obtained without scaling the motion vector of thecollocated block; wherein the motion vector predictor of the currentblock is determined from among motion vector prediction candidates,comprising the temporal motion vector prediction candidate wherein thescaling is based on a ratio of a distance (Td) between the collocatedpicture and the reference picture of the collocated block and a distance(Tb) between the current picture and the reference picture of thecurrent block.